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Ms, Kerry Heckman 3 - 1 June 2006 2211 N. Wilson Way, Stockton, San Joaquin County 4) The OPS of the Workplan will require submittal of an addendum to the Workplan to address the comments listed below. Please provide an OPS addendum to the Workplan by 30 June 2006 to address the comments listed below. A). An eighteen injection well pilot study seems excessive when compared to other pilot studies. Provide a rationale for the large number of injection wells, or scale down the pilot study to use fewer injection wells. B). All of the injection wells are drawn with a 10-foot radius of influence (Figure 3). The Workplan does not provide the engineering calculations to support a 10-foot radius of influence design. Provide the engineering calculations, based on an analysis of soil sampling conducted during the BST and available geotechnical and hydrogeological data, for the radius of influence of the injection wells. C). Provide cross-section(s) to complement Figure 3, to facilitate viewing placement of the injection points in three dimensions. Include soil and sediment descriptions (lithology) and monitoring well concentrations of the targeted hydrologic zones in the cross-section(s). D). Provide a schematic drawing of the ozone injection system, including the location of the ozone generator and all piping runs to the ozone injection points. E). Figure 4 is a schematic of a generic Air Sparge Well, which has been modified for the ozone injection points. Provide a detail drawing or photograph of the 2 inch Polyvinyl Chloride 50 micron (Schedule 40) sparge point shown at the bottom of the well. Is this device in direct contact with the well filter pack, or is it recessed inside of a well screen? F). rage 12 states the pilot study will last O I lol IU IJ, dl WHICH I UI11C a rel V111111c1 Iu0L1U11 may be made to expand the Ozone injection system. The pilot study should provide progress reports in addition to the final report at 6 months. Provide a schedule for the pilot study and include a discussion of the results of monthly sampling in the Quarterly Monitoring Reports prior to the final report. G). Add hexavalent chromium, bromide, and bromate to the list of OPS analyses. 5) Page 12 details the installation of 3 additional 200-foot deep monitoring wells, to complete the characterization of the dissolved phase groundwater plume. After reviewing the proposed monitoring well locations on Figure 3, and comparing the Report Table 4 for concentrations in nearby monitoring wells, I question the need for the proposed monitoring wells at the proposed locations. Source area monitoring well MW-37 (screened 195 to 200 feet bgs) has always been Non-Detect for all constituents over 7 quarters; source area MW-35 (243-248 feet bgs) has been ND for the last 5 quarters. The existing wells to the south of the Site (MW-43, screened 90-100 ft bgs and MW-44, screened 140-150 ft bgs) are showing decreasing 1,2-DCA concentrations after two quarters of monitoring (from 6.7 pg/L to <0.5 pg/L and from 18 pg/L to 4.2 pg/L, respectively), which may indicate vertical and lateral definition to the south. In a similar fashion to the north, deeper MW-45 (screened 140-150 ft bgs) and MW-46 (screened 90-100 ft bgs) are, respectively, non-detect (<0.5 pg/L) at depth or showing stable 1,2-DCA concentrations (13 pg/L) after two quarters of monitoring. Finally, while MW-38 (screened 90-100 ft bgs) increased from non-detect to 310 pg/L over two quarters of monitoring, adjacent deeper MW-39 (screened 140-150 ft bgs) has been non-detect (<0.5 pg/L) over the same period. Considering the current results, I request that at least two more quarters of sampling, for a total of one hydrologic cycle