FIELD DOCUMENTS AND WORK PLANS 2004-2014

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Steve Ross January 11,2008 DTSC—RTCs for RAIWP Approval Letter Page 2 collect depth discrete samples from these wells at different depths within the screens. This sampling could be done with micropurging methods and possibly with the use of packers to help minimize mixing of groundwater. Response: The two wells discussed in the comment(MW-213 and MW-214)are designed as intermediate extraction wells and are currently being utilized for groundwater extraction and treatment. As groundwater concentrations approach cleanup goals in these wells SPX will evaluate and consider depth discrete sampling for chromium in wells MW-213 and MW-214. Comment 3: A review of Figure 8 indicated that deep zone monitoring well MW-460 was not sampled. This well could be important to assess the vertical migration of chromium from the intermediate zone to the deep zone. Recommend collecting regular scheduled groundwater samples from MW-460. Response: Well MW-460 has been sampled as recently as April 2007 as part of the former MRP conducted by Dudek. This well was monitored and sampled annually as part of the former program. At this time SPX does not feel it is necessary to incorporate additional sampling of MW-460 because historically dissolved chromium has not been reported in this well. Well MW- 460 is screened below a reduced environment (Blue Clay hydrogeologic unit) in which hexavalent chromium is not chemically stable and converts to trivalent chromium. Well MW- 424(I-2)is screened above well MW-460. In April 1989 well MW-424 had dissolved chromium detected at concentrations of 2,960 ug/L and chromium was not detected in well MW-460. During the April 2007 groundwater sampling event dissolved chromium concentrations were reported < 10 ug/L collected from well MW-424 and MW-460. This data suggests that even if relatively high concentrations of dissolved chromium was present in the intermediate zone vertical migration would not be observed due to the geochemistry between and within the intermediate and deeper zone. Comment 4: Well locations proposed for background and compliance well monitoring are for the shallow zone.Recommended including background and compliance well monitoring in the 100-foot sand and intermediate zones. Response:At the recommendation of the DTSC, SPX is prepared to add 100 foot sand zone well MW-310 and intermediate zone wells MW-1, MW-211, and MW-325 to the list of background and compliance wells to be sampled for the program. Comment 5: Copy DTSC on all documents transmitted to the Central Valley Regional Water Quality Control Board associated with compliance to Waste Discharge Requirements Order Number R5-2007-0126. Response: The comment is noted.