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water Levels beneath the trees near these cells (see Figure 1 for locations of recharge basins). <br />Pre-mine groundwater levels will be evaluated through groundwater monitoring. <br />Groundwater Monitoring <br />Thirty monitoring wells (AMEC 2005) have been installed at, and adjacent to, the site. Water <br />level monitoring in the 30 wells will be conducted on a monthly basis for five quarters prior to <br />mining to establish asite-wide baseline. Once mining begins, monitoring will be conducted on a <br />monthly basis for the first year (during dewatering), and on a quarterly basis thereafter until two <br />years after the mining in a particular phase ends. Table 1 presents the wells associated with each <br />mine phase. <br />Reporting <br />Prior to mining, Lafarge will prepare and submit a report on baseline groundwater levels, based <br />on data from the 30 existing wells. Thereafter, groundwater monitoring data will be submitted <br />with the annual progress report to the DMG and copied to Weld County Planning and <br />Engineering Deparhnents. At least five quarters of monitoring data will be obtained prior to <br />mining each phase. <br />Wells Within 600 Feet <br />Owners of all water supply wells within 600 feet of extraction cells will be contacted and asked <br />to sign a 600-Foot Well Spacing Statement. If the owners indicate that the wells aze in use, <br />Lafarge will attempt to measure well depth, pumping rate, pumping water level, and non- <br />pumping water level prior to mining. Additionally, to establish a baseline, Lafarge will attempt <br />to measure water levels in these wells monthly prior to mining. After mining begins, Lafarge <br />will attempt to measure water levels in the existing water supply wells quarterly, until two years <br />after mining. <br />MITIGATION <br />Monitoring data will be used to identify potential changes in alluvial groundwater flow or <br />elevation associated with mining and reclamation activities. Baseline data collected from the <br />monitoring program will provide a range of relative water levels associated with pre-mining <br />groundwater conditions. Experience at other sand and gravel mine sites in similar geologic <br />settings has found that groundwater levels tend to fluctuate between two to four feet each year, <br />being highest in the summer and lowest in the winter and early spring. <br />WELLS <br />If, during mining, the relative seasonal groundwater elevation at any of the domestic <br />wells or monitoring wells adjacent to domestic wells differs from the baseline conditions <br />by more than two feet, and the condition was not observed during baseline monitoring, or <br />if Lafarge receives a complaint from any well owner within 600 feet from the site <br />Lafarge West, Inc. Riverbend - 3 - August 2005 <br />Groundwater Monitoring andMitiga[ionPlan H:bt37_012_02\(iro~mdwan:rUtiverbendGWMOn&MifigationPlanB•26-OS.dac <br />