2005-10-24_REVISION - M2000016 (2)

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The objectives of the well installation and monitoring program are to monitor the current groundwater conditions and to provide a basis for assessing the future impacts of the proposed mining on nearby wells and trees. Through the well monitoring program, pre-mining groundwater elevations, flow patterns across and near the property, and seasonal fluctuations are being documented. The additional wells requested by the DMG will be installed in phases consistent with the mining phases. The wells will be installed 18 months prior to the start of mining to allow the collection of five quarters of monitoring data. Well Inventory A well inventory (AMEC 2005) of the site and adjacent areas was conducted to identify wells near the project. The inventory involved review of well records (Registered Wells) on file with the Colorado Department of Natural Resources, Office of the State Engineer (SEO). The search area of the well inventory was 1,500 feet from the property boundary. As required by the SEO, Lafarge will attempt to get a 600-foot well spacing agreement statement from the well owners who have wells within 600 feet at least six months prior to the commencement of mining of a relevant phase. The well inventory identified a total of 13 wells within 600 feet of the site boundary. Lafarge either owns or has a lease agreement with 9 of the 13 wells. Consequently, only four wells will require the 600-foot well spacing agreement and/or mitigation measures. Prior to mining, Lafarge will field check the location of wells, registered and unregistered, and document the location, ownership and contact information for the wells. Modeling During 2005, a numerical groundwater flow model was constructed of the site and surrounding areas to assess the potential impacts that the mine operation may have on groundwater levels (AMEC 2005). The U.S. Geological Survey's groundwater code MODFLOW (McDonald and Hazbaugh, 1988) was used for the modeling. The groundwater investigation and modeling of the site concluded that the water table occurs at depths of approximately five to ten feet below ground surface during the irrigation season. The thickness of saturated alluvial sediments ranges from approximately 20 to 40 feet. The typical groundwater flow direction is to the north along the South Platte River, but directions and gradients vary locally and seasonally due to changing irrigation patterns and pumping of irrigation wells. MONITORING AND MANAGEMENT Mining Plan The Mining Plan has been designed to reduce goundwater impacts to adjacent properties to the geatest practical extent. The extraction cells will be dewatered with each phase of mining. Lafarge proposes to construct recharge basins along the boundaries o£ Cell 1 Plant Area, Cell 1 Phase 4, Cell 1 Phase 2, Cell 1 Phase 3, Cell 1 Phase 5, Cell 1 Phase 6 to maintain pre-mine Lafarge West, Inc. Riverbend - 2 - October 2005 Groundwater Monitoring and Mitigation Plan fa:~a~37_oi2_o2!croundwarenRiverbend Gw Mon .@MitigaNon Ptan sa6-os.aoc