2005-10-24_REVISION - M2000016 (2)

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water levels beneath the trees near these cells (see Figure 1 for locations of recharge basins), Pre-mine groundwater levels will be evaluated through groundwater monitoring. Groundwater Monitoring Thirty monitoring wells (AMEC 2005) have been installed at, and adjacent to, the site. Water level monitoring in the 30 wells will be conducted on a monthly basis for five quarters prior to mining to establish asite-wide baseline. Once mining begins, monitoring will be conducted on a monthly basis until a steady state condition is reached (during dewatering), and on a quarterly basis thereafter until two years after the mining in a particular phase ends. Each mining phase will be evaluated on a case-by-case basis to determine if a less frequent monitoring schedule is appropriate. If this is found to be the case, then Lafazge will submit a Technical Revision request to the Division of Minerals and Geology to relax the groundwater monitoring requirements in those certain areas. Table 1 presents the wells associated with each mine phase. Reporting Prior to mining, Lafarge will prepaze and submit a report on baseline groundwater levels, utilizing data from the 30 existing wells. Thereafter, groundwater monitoring data will be submitted with the annual progress report to the DMG and copied to Weld County Planning and Engineering Deparhnents. At least five quarters of monitoring data will be obtained prior to mining each phase. If any of the following trigger points are reached: • A complaint from a well owner within 1,500 feet of the site boundary, • The relative seasonal groundwater level at any of the domestic wells or monitoring wells adjacent to domestic wells differs from the baseline conditions by more than two feet, • Or the qualified individual inspecting adjacent off-site vegetation denotes stressed vegetation, then Lafazge will submit their groundwater monitoring data to the DMG immediately. Copies will also be provided to Weld County Planning and Engineering Departments. Wells Within 600 Feet Owners of all water supply wells within 600 feet of extraction cells will be contacted and asked to sign a 600-Foot Well Spacing Statement. If the owners indicate that the wells are in use, Lafarge will attempt to measure well depth, pumping rate, pumping water level, and non- pumping water level prior to mining. If well owners are unwilling to allow Lafarge access to their wells to gather the necessary measurements, then Lafarge will install a monitoring well between the well and the mine. Additionally, to establish a baseline, Lafarge will attempt to measure water levels in these wells monthly prior to mining. After mining begins, Lafarge will attempt to measure water levels in the existing water supply wells quarterly, until two years after mining. MITIGATION Monitoring data will be used to identify potential changes in alluvial groundwater flow or elevation associated with mining and reclamation activities. Baseline data collected from the Lafarge West, Inc. Riverbend - 3 - October 2005 GrOUndwater Monitoring and Mitigadon Plan H:W137_012_02\Groundwaler\Riverbend GW Mon & Mitigation Plan 8-2605.doc