2019-11-12_REVISION - M2004044 (13)

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Jared Ebert November 8, 2019 Page 2 of 6 Al will bear the cost of installing and operating the cisterns. If the wells are completely dewatered and it is not practical to replace the existing wells with deeper or more efficient wells, Al will deliver potable water to the cisterns for the duration of the impacts. As indicated above Al may improve the existing wells to provide water to the cistern rather than continue to haul water for an extended period of time. In any event Al will provide potable water to the well owner. e. DRMS Response(3): Please provide documentation that the affected well owners have agreed to the proposed mitigation plan. Al Response: Copies of the executed agreements with the affected wells owners are attached. 16. Page G-4, the Potential Mining Impacts section is confusing and hard to follow. Overall, the points made in this section are unclear. Please revise this section to clarify the statements made. The Division recommends addressing the impacts from dewatering and slurry wall installation (mounding and shadowing) by clearly indicating the possible impacts and their associated severity. If conclusions about the mining impacts are taken from the groundwater study, please make this clear and cite specifically where within the report these conclusions are addressed. c. Al Response: Please see the revised Exhibit G Sections 2 (b), and Potential Mining Impacts. d. DRMS Response: Revised page G-5 indicates ground water will mound up to approximately six feet along the western and southern edges of the West Mine Area. According to recent monitoring data, water levels can range from eight to nine feet below the ground surface in this area. A rise of six feet after the installation of the slurry wall is significant given the current shallow depth of groundwater. Given this, the Division will require preemptive mitigation. Please provide designs and plans for an appropriate drainage system that will maintain the historic groundwater levels after the installation of the slurry wall. Please commit to installing the drainage system concurrently with slurry wall installation. e. Al Response: Al is committed to installing an underdrain system to minimize disturbances to the prevailing hydrologic balance of the ground water regime near the mine. Groundwater modeling indicated mounding up to approximately six feet will likely occur along the west and south west margins of the West Mine Area. A preliminary design is shown in plan view and cross sections on Figure G-2 through G-5. Please note that this design is preliminary,and may change after the final determination of the location of the slurry wall. The drain system will consist of three sections, South Side Drain, West Drain South Reach and West Drain North Reach. Each drain has a "receiving" section and a "discharging" section. In the"receiving' sections the drain will be installed at approximately the pre-mining ground water level. As the mound builds it will flow into the drain pipe. In non-mounding areas the "discharging "sections the drain pipe will be at or approximately one foot above the pre-mining ground water levels. In the areas of the ground water mound the ground water will flow into the drain then flow down gradient through the drain pipe and discharge back to the ground water. The entire length of the drain pipe will be perforate. The slope of the drain pipe and seasonal Aggregate Industries—WCR,Inc 1687 Cole Blvd Suite 300 Golden,CO 80401