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IRM Prove-Out Reports -3- 29 August 1991 DDRW, Tracy reported problems and therefore, should not prevent the initiation of the Full- Scale Operation of the IRM. 8. Page 10. The report states that the Prove-Out Phase of the IRM was conducted between 11 to 15 April 1991 . However, the report had previously indicated that the Prove-Out Phase had begun on 12 April 1991 (pages 7 and 8) . This discrepancy in the dates needs to be clarified. INSTALLATION DATA REPORT 1. Page 2. The rationale for the placement of the injection wells in the northwestern corner of the site was not discussed in the report, other than to state that these wells were placed in an uncontaminated area. It is unknown whether the northwest corner was selected due to potential on-site access restrictions, to the lithoiogy in that portion of the site, to the affects of the injected water on the gradients and plume movement, or for some other reason. The rationale for the placement of the injection system should have been discussed. 2. Page 2. The rationale for the placement of the monitor wells for the extraction and injection systems in the up gradient direction rather than the down gradient direction was not discussed. It would be expected that the maximum hydraulic effects of both the extraction and injection would be observed in the down gradient direction. However, because the wells are located along the northern boundary of the site, off-site accessibility may have been the controlling factor in the placement of these monitor wells. The rationale behind the placement of the wells should have been discussed in the report. 3. Page 3. The report states that only five wells were drilled for the extraction system. One of the existing wells was to be used for extraction (EW-1) . Information on the construction of EW-1 was not provided in the report. The lack of information on this well appears to be an example of the absence of an exchange of data between Tracy's contractors for the IRM and the RI/FS. 4. Page 3. The rationale for the placement of the extraction wells 100 feet apart and approximately 45 feet in depth was not discussed in the report. It is unknown whether 100 feet is an optimal distance between wells to create a hydraulic barrier at the boundary of the site and whether the depth of 45 feet was at the highest volatile organic constituent (VOC) concentrations in the plume. The criteria for the lateral and vertical placement of these wells should have been discussed. 5. Pages 3 and 12. The rationale for the selection of the screen length on the extraction and injection wells was not discussed. The extraction wells were installed with a 20 foot screen lengths and the injection wells were installed with a 50 foot screen lengths. It is unknown whether the 20 foot length covers all of the uppermost gravel layer and how the 20 feet relates to the vertical distribution of the contamination. It is unknown why a total of 50 feet of screen was used for the injection wells. Based on the performance of EW-2 during the Start-Up Phase, this screen length may not have been adequate. The report did not clearly indicate whether the final selection of the screen length was based on lithology. The report should have provided more discussion on the selection of screen lengths for the injection and extraction wells.