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Review of the Draft Extraction Well Optimization Work Plan, <br /> DDJC-Sharpe, <br /> Lathrop, California <br /> September 2005 <br /> GENERAL COMMENTS <br /> 1. The principal concepts presented in this Draft Extraction Well Optimization Work Plan <br /> (Work Plan) appear to be reasonable and technically sound, however, final acceptance <br /> must be deferred until review of the results of the Defense Distribution Depot San <br /> Joaquin California(I)DJC)-Sharpe groundwater modeling has been completed. <br /> 2. The text in the Work Plan discusses reducing the number of extraction wells to 15 with <br /> one alternate well, however, the alternate well is not discussed in the text. The <br /> information presented in Table 1 appears to indicate that the alternate well is EWNC3R. <br /> Please provide some discussion in the text of the Work Plan about the decision logic that <br /> will be used to initiate operation of the alternate well. <br /> SPECIFIC COMMENTS <br /> 1. Section 3.1.2,Page 4: The text in the first part of this section states that long-term <br /> containment of groundwater contaminant plumes is a prerequisite to the optimization <br /> process, but the second-to-last sentence implies that the purpose of the containment is to <br /> prevent contaminated groundwater from reaching additional potable supply wells. The <br /> groundwater remedy at DDJC-Sharpe as described in the Record of Decision (ROD)is <br /> designed to restore groundwater to beneficial uses, not merely to prevent migration to <br /> supply wells. Please explain the reference to plumes reaching potable supply wells or <br /> reword the sentence to be consistent with the objectives of the ROD. <br /> 2. Section 3.1.4,Page 5: The text in this section states that shutting down potable water <br /> supply wells will decrease the westward hydraulic gradient caused by their pumping, but <br /> earlier sections (ES.3, 1.3) discuss that shutting these wells and the DDJC-Sharpe <br /> extraction wells will decrease the easterly gradient, potentially decreasing the rate of <br /> migration of the saline front. Please provide a brief description of the hydraulic influence <br /> of these wells so that readers will clearly understand how they are creating a westward <br /> gradient and an easterly gradient. <br /> 3. Figure 2,Page S: EWCA1 is shown as one of the wells proposed for optimization, but <br /> no estimated capture zone is shown for this well. Please revise the figure to show the <br /> estimated capture zone of EWCA1 or explain why a well with no apparent capture is <br /> being retained for optimization. <br /> 4. Figure 4,Page 10: EWC4 is shown as one of the wells proposed for optimization, but its <br /> estimated capture zone does not indicate that the current C-zone plumes of <br /> trichloroethene and tetrachloroethene are currently being captured by this well. Please <br /> explain if plans for optimization include increasing pumping rates or installing new wells <br /> if needed to provide capture at the facility's western boundary. <br />