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matter of days. Trenching for burial and winterization of existing piping systems is currently <br />underway. Freezing conditions can occur at any time beginning in the month of October and <br />based on historical stream flow patterns, water tables in the alluvial fill are expected to begin <br />rising soon. These factors could significantly complicate and hamper trenching and new sump <br />installation efforts. For all of the above reasons, Cotter requests that this Technical Revision be <br />reviewed and approved by DRMS as quickly as possible so that sump construction and <br />installation can begin promptly. <br />The planned location of the first additional sump / French drain system (termed "Sump 5") is <br />shown in Figure 3. Additional piping system infrastructure will be planned and built into the <br />alluvial trenching network in the general vicinity of potential additional sump locations to <br />minimize installation lead time, should additional extraction zones be necessary to provide <br />sufficient hydraulic capture capacity to meet stream water quality standards in Ralston Creek. <br />Various hydrologic factors will be carefully evaluated in selection of any additional alluvial <br />groundwater extraction locations, including results of a new stream survey to be performed <br />between SW-BOS and SW-BPL. The study will be conducted on a single day to minimize <br />potentially confounding effects of parameters that may have significant spatial and temporal <br />variability. Survey parameters at each location will include stream flow, stream water uranium <br />concentration, electrical conductivity, and qualitative indications of localized groundwater <br />inflows (such as moist patches of soil/sediment and vegetative indicator species). <br />Based on current information, areas expected to be considered for additional sump locations are <br />shown as green shaded areas in Figure 3. Accordingly, Cotter requests that this Technical <br />Revision provide flexibility with respect to potential future expansion of the alluvial groundwater <br />capture capacity of the system. A general engineering design of a proposed sump/French drain <br />system is provided in Attachment 1. Pumps and pumping infrastructure will be similar to that <br />currently installed at Sumps 1 and 4. <br />In addition to the above Technical Revision requests, it is proposed that a small, minimally <br />engineered temporary pumping system be immediately placed in the seasonal pond formed by <br />alluvial groundwater that "daylights" through seeps within excavated portions of the former <br />overflow retention pond (Figure 3). Due to potential future remedial actions in the vicinity of <br />this pond or related uses of this area (e.g. adjacent excavations and/or use as temporary storage <br />or fill capacity for excavated materials), this pumping system may not be fully trenched or <br />winterized, but could strategically operate when feasible, for example during seasonal periods of <br />non-freezing conditions or high water tables. This measure is expected to create a partial <br />hydraulic barrier that minimizes groundwater flow inputs into the alluvial fill. <br />4