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1 ~. <br />1I IA <br />' of groundwater thereby ensuring compliance with the CDO and enhancing overall water ^ <br />/N.D ~.~,,y! <br />' managemen~e construction of the slurry wall is subject to regulatory review and approval b}~~ (~'' <br />r ~µ~ <br />the DMG.. The second phase will consist of operation of an active water treatment facility under .tt t~, f( <br />' a final CDPS permit and will be implemented as soon as requisite permits aze obtained and the <br />first phase is completed. The third phase would consist of maintaining the modified hydrologic <br />' conditions that will develop as a result of implementation of this response plan. These phases are <br />designed to: (1) achieve the initial goal of the response plan, which is to conhol the flow of <br />groundwater from the West Pit, (2) maintain containment of groundwater in the West Pit, and (3) <br />implement long-term recovery of the hydrochemistry in the West Pit backfill. <br />' Throughout all phases of the response program, groundwater will be removed from the backfill <br />' in order to reverse and maintain the hydraulic gradient between the West Pit and the Rito Seco. <br />The goal of the gradient reversal is to control groundwater flow from the West Pit to the Rito <br />' Seco alluvial system. Details of the response actions are discussed in the following; sub-sections. <br />' 2.0 PROPOSED RESPONSE PLAN <br />The hydrologic system in the vicinity of the West Pit is described in detail in Section 3.1 of TR- <br />' 26. Conceptually, the flow of water in the vicinity of the West Pit represents an open system in <br />that water flows into the West Pit from two principal sources (the Precambrian bedrock aquifer <br />' and the Rito Seco alluvial aquifer on the east side of the West Pit) and groundwater flows out the <br />West Pit through a restricted zone on the southeastern side of the West Pit. Some of the <br />' hydrologic flows in the vicinity of the West Pit can be managed (e.g., the outflow of groundwater <br />' from the West Pit), but other hydrologic flows cannot be reasonably modified (e.€.., inflow from <br />the Precambrian bedrock aquifer). As a result, the response plan is constrained t!y the existing <br />' hydrologic conditions and any modification to the existing hydrologic system may have <br />consequences on other parts of the groundwater system in the vicinity of the West ?it. The water <br />' management plan outlined in Section 6 of TR-26 calls for lowering the water level in the West <br />Pit backfill to an elevation that will reverse the hydraulic gradient between the backfill and the <br />' Rito Seco alluvial aquifer. The characterization and analysis of the hydrologic system as <br />' <br />Ba!!le Mountain Resources, /nc. <br />' n~roiy.s~Kiraozenrrpkimormr~..r~~ ~p~~ro~e{da 3 Shepherd hfdler, /nc. <br />September l7, 1999 <br />