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Mr. Jared Ebert <br /> RE: Lamb Lakes Site M-2018-039 <br /> October 15, 2018 <br /> 7. The Lamb Lakes Groundwater Monitoring Plan shall be established, incorporating the <br /> recommendations presented in the Hydrogeologic Evaluation (Attachment B). The <br /> recommendations include installation of eight monitoring wells, a minimum of 18 months <br /> baseline data collection prior to additional mining and reclamation activities, and a <br /> quarterly monitoring frequency. The monitoring plan shall be used prior to, during, and <br /> following mine operations and reclamation activities at the Lamb Lakes site and shall <br /> evaluate potential mining and reclamation impacts. <br /> The monitoring plan shall include the installation of new alluvial wells or, if constructed <br /> appropriately, existing alluvial wells. The wells/piezometers shall be installed as soon as <br /> is practical so that baseline groundwater elevation data can be collected prior to new <br /> mining and reclamation activities. The monitoring plan, including details of well <br /> installation and surveyed well locations and elevations, shall be submitted to the <br /> Division. Additionally, once baseline data has been collected and typical groundwater <br /> elevation fluctuations can be evaluated, elevations associated with potential impacts shall <br /> be established. The monitoring plan shall be updated with the baseline data evaluation <br /> and potential impact "trigger" elevations and submitted to the Division prior to new <br /> mining and reclamation activities. All routine monitoring data shall be provided to the <br /> Division during annual reporting. <br /> 8. The aquifer affected by the Lamb Lakes mining and reclamation activities is the Cache la <br /> Poudre alluvial aquifer. No other aquifers shall be affected by the operation. <br /> 9. Prior to dewatering and any mining or other site construction activities below the <br /> groundwater table, the site SWSP shall be updated with the SEO to cover all associated <br /> depletions. <br /> 10. Water consumed during mining and slurry wall construction activities will include <br /> evaporation from exposed groundwater in dewatering trenches and potential settling <br /> basins as well as additional operational water losses from dust control and water retained <br /> in mined material hauled off-site or placed above the groundwater table. Estimates are <br /> based on only one lake being dewatered and one slurry wall being constructed per year. <br /> According to initial estimates, the maximum annual consumptive use in the proposed <br /> permit area is 10.5 acre-feet. This depletion is based on approximately 3 acres of <br /> exposed groundwater area for dewatering trenches and settling basins and a net <br /> evaporative loss of approximately 2.6 acre-feet per year. If the moisture content of the <br /> material transported off-site or placed above the groundwater table is assumed to <br /> be 4 percent by weight, and the annual mined material from the pit bottom is estimated to <br /> be 200,000 tons per year, then the annual amount of water lost in material <br /> is approximately 5.9 acre-feet. It is also estimated that approximately 2 acre-feet of water <br /> will be needed annually for dust control during mining and reclamation activities. A new <br /> SWSP for evaporation and operational losses will be obtained from the SEO prior to any <br /> new activities below the groundwater table. <br /> Page 4 of 7 <br />