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/ _. <br />The objectives th-e well installation and monitoring program aze to monitor the current <br />groundwater co ditions and to provide a basis for assessing the future impacts of the proposed <br />mining on riet"~rby,wells and trees. Through the well monitoring program, pre-mining <br />groundwater elevations, flow patterns across and near the property, and seasonal fluctuations aze <br />being documerited~~ <br />~~ <br />TIIe additional wells requested by the DMG will be installed in phases consistent with the mining <br />phases. The wells will be installed 18 months prior to the start of mining to allow the collection <br />of five quarters of monitoring data. <br />Well Inventory <br />A well inventory (AMEC 2005) of the site and adjacent areas was conducted to identify wells <br />near the project. The inventory involved review of well records (Registered Wells) on file with <br />the Colorado Department of Natural Resources, Office of the State Engineer (SEO). <br />The search area of the well inventory was 600 feet from the property boundary. The well <br />inventory identified a total of 13 wells within 600 feet of the site boundary. Lafarge either owns <br />or has a lease agreement with 9 of the 13 wells. Consequently, only four wells will require the <br />600-foot well spacing agreement and/or mitigation measures. As required by the SEO, Lafarge <br />will attempt to get a 600-foot well spacing agreement statement from the well owners of the four <br />wells. Prior to mining, Lafazge will field check the location of wells, registered and <br />unregistered, and document the location, ownership and contact information for the wells. <br />Modeling <br />During 2005, a numerical groundwater flow model was constructed of the site and surrounding <br />areas to assess the potential impacts that the mine operation may have on groundwater levels <br />(AMEC 2005). The U.S. Geological Survey's groundwater code MODFLOW (McDonald and <br />Harbaugh, 1988) was used for the modeling. <br />i <br />The groundwater investigation and modeling of the site concluded that the water table occurs at <br />depths of approximately five to ten feet below ground surface during the irrigation season. The <br />thickness of saturated alluvial sediments ranges from approximately 20 to 40 feet. The typical <br />groundwater flow direction is to the north along the South Platte River, but directions and <br />gradients vary locally and seasonally due to changing irrigation patterns and pumping of <br />irrigation wells. <br />MONITORING AND MANAGEMENT <br />Mining Plan <br />The Mining Plan has been designed to reduce groundwater impacts to adjacent properties to the <br />greatest practical extent. The extraction cells will be dewatered with each phase of mining. <br />Lafarge proposes to construct recharge basins along the boundaries of: Cell 1 Plant Area, Cell I <br />Phase 4, Cell 1 Phase 2, Cell 1 Phase 3, Cell 1 Phase 5, Cell I Phase 6 to maintain pre-mine <br /> <br />Iafazge West, Inc. Riverbend - 2 - August 2005 <br />Groundwater Monitoring and Mitigation Plan H:W 137_012_02\GmwdwaterUtive`bend CW Mon & Mitigation Plan 5-2605.doc <br />