2021-09-09_REVISION - M2004044 (10)

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The drawdown estimated by the model assumes the wells were pumping at the Aurora property Greenhouse and one domestic well north of the mine. Given that the greenhouse wells will not be pumping, the drawdown will likely be less than the of six to eight feet estimated by the model. There is one remaining domestic alluvial water well in this strip of land. Potential impacts to the well will be addressed by the Ground Water Mitigation Plan. Groundwater Mitigation Plan Groundwater monitoring and evaluation of potential mining or reclamation impacts shall be conducted as part of the Groundwater Monitoring and Mitigation Plan. The Monitoring Plan was reviewed and approved by the Division with the original permit and will be used during mining and reclamation activities. Historic and current water level measurements in the monitoring wells included as part of this exhibit. The Monitoring Plan is outlined below. It is possible that the well north of the site may be impacted by shadowing effects of the slurry wall. If the wells fail to perform at historic rates, Al will make investigations into the cause. If the cause can be traced to the mine and slurry wall, Al will make efforts to improve the wells either by several alternatives including: discharging water near the well, developing the well to remove scales and plugs, deepening the well, and/or constructing cisterns and delivering potable water to the cisterns for the duration of the impacts. As indicated above Al may improve the existing wells rather than continue to haul water for an extended period. In any event Al will provide potable water to the well owner. 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. The design plans are attached to this exhibit. The drain system will consist of two sections, South Side Drain and a West drain that conveys water along the north side of the West Mine Area. 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 drainpipe. In non-mounding areas the "discharging "sections the drainpipe will be at or approximately one foot above the premining 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 drainpipe and discharge back to the ground water. The entire length of the drainpipe will be perforated. This design concept has been utilized at the Aurora Challenger Pit just north of the West Mine Area. To establish a baseline, Al installed 17 monitoring wells at the mining site in late 2003. The frequency of water level monitoring was approximately monthly from December 2003 to July 2005. After July 2005, monitoring continued quarterly through 2017. The monitoring frequency increased to monthly in January 2018. Monitoring in the wells will continue on a monthly basis for the life of the mine and for one year after mining ends. (Note: MW-11 was removed during Todd Creek Metropolitan District's construction in 2017 and MW-2 south of the mine can no longer be found). MW-2 was I replaced with a Aggregate Industries—Tucson South Amendment—MLRB 112 Permit Application Exhibit G-7