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Jared Ebert <br /> September 16,2019 <br /> Page 4 of 11 <br /> Tech and a local driller familiar with the wells in the area. Al will bear the cost of installing and operating <br /> the cisterns. If the wells are completely dewatered and it is not practical to replace the existing wells <br /> with deeper or more efficient wells, Al will deliver potable water to the cisterns for the duration of the <br /> impacts. As indicated above Al may improve the existing wells to provide water to the cistern rather <br /> than continue to haul water for an extended period of time. In any event Al will provide potable water to <br /> the well owner. <br /> 16. Page G-4, the Potential Mining Impacts section is confusing and hard to follow. Overall, the points <br /> made in this section are unclear. Please revise this section to clarify the statements made. The Division <br /> recommends addressing the impacts from dewatering and slurry wall installation (mounding and <br /> shadowing) by clearly indicating the possible impacts and their associated severity. If conclusions about <br /> the mining impacts are taken from the groundwater study, please make this clear and cite specifically <br /> where within the report these conclusions are addressed. <br /> a. Al Response: Please see the revised Exhibit G Sections 2 (b), and Potential Mining Impacts. <br /> b. DRMS Response: Revised page G-5 indicates ground water will mound up to approximately six feet <br /> along the western and southern edges of the West Mine Area. According to recent monitoring data, <br /> water levels can range from eight to nine feet below the ground surface in this area. A rise of six feet <br /> after the installation of the slurry wall is significant given the current shallow depth of groundwater. <br /> Given this, the Division will require preemptive mitigation. Please provide designs and plans for an <br /> appropriate drainage system that will maintain the historic groundwater levels after the installation of <br /> the slurry wall. Please commit to installing the drainage system concurrently with slurry wall installation. <br /> Al Response: Al is committed to installing an underdrain system to minimize disturbances to the <br /> prevailing hydrologic balance of the ground water regime near the mine. Groundwater modeling <br /> indicated mounding up to approximately six feet will likely occur along the west and south west margins <br /> of the West Mine Area. A preliminary design is shown in plan view and cross sections on Figure G-2 <br /> through G-5. Please note that this design is preliminary and may change after the final determination of <br /> the location of the slung wall. <br /> The drain system will consist of three sections, South Side Drain, West Drain South Reach and West <br /> Drain North Reach. Each drain has a "receiving" section and a "discharging" section. In the"receiving' <br /> sections the drain will be installed at approximately the pre-mining ground water level. As the mound <br /> builds it will flow into the drain pipe. In non-mounding areas the"discharging "sections the drain pipe <br /> will be at or approximately one foot above the pre-mining ground water levels. In the areas of the <br /> ground water mound the ground water will flow into the drain then flow down gradient through the drain <br /> pipe and discharge back to the ground water. The entire length of the drain pipe will be perforate. The <br /> slope of the drain pipe and seasonal high and low water levels are shown on the drain profiles. This <br /> design concept has been utilized at the Challenger Pit just north of the West Mine Area. <br /> Aggregate Industries—WCR,Inc <br /> 1687 Cole Blvd Suite 300 <br /> Golden,CO 80401 <br />