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Page 3 <br /> Mr.Mark Johnson <br /> January 31,2020 <br /> Potential Slurry Wall&Mining Impacts to Local Groundwater Levels <br /> For all lined cells, a properly constructed slurry wall or compacted clay liner will tend to isolate these cells <br /> from the surrounding alluvial groundwater table.The liner around these cells could cause"mounding"of <br /> groundwater(increase in groundwater elevation)on the upgradient side(south and southwest)of the lined <br /> cells and a potential"shadow effect"(reduction in groundwater level)on the downgradient side(north and <br /> northeast)of the Mine. Because the liner will tend to isolate these cells from the surrounding groundwater <br /> table,the effects of dewatering when mining lined cells will tend to not extend beyond the liner. <br /> Any mounding effect on the upgradient side of the south and southwest is anticipated to be on the order of a <br /> few feet or less and will dissipate with distance from the mine. Similarly shadowing affects will be on the <br /> order of a few feet and will dissipate with distance from the mine. The shadowing affects will be minimized <br /> by the presence of the Saint Vrain River on the north and the presence of the Rural and Last Chance <br /> ditches between the cells. <br /> Dewatering of the unlined cells(Cell 1 and Cell 2b)will result in decreases in water levels around these <br /> cells. Five(5)wells are permitted within 600 feet of Cell 1. No wells are permitted within 600 feet of Cell 2b. <br /> These wells and potential mitigation measures are discussed below. <br /> Area Wells <br /> A review of permitted wells on file at the State engineer's Office(SEO), Division of Water Resources(DWR) <br /> indicates there are five(5)permitted pumping wells within 600 feet of the permit boundary. All of these <br /> wells are screened in the alluvium. Three(3)of these wells, are west(upgradient)of the unlined Cell 1,one <br /> (1)well is downgradient of Cell 1,and one(1)well is within the mine area and is owned by the Vogls. <br /> A discussion of the wells located within 600 feet of the permit boundary are discussed below: <br /> ➢ Lee Well: The Lee well is located south and east of the intersection of Weld County Roads 24'/4 <br /> and 11 '/4. This well is approximately 300 feet and cross gradient of Cell 1 and may be affected by <br /> dewatering of Cell 1. <br /> ➢ Neumann Well: The Neumann well is located west of the site on the north side of Weld County <br /> Road 24%. This well is approximately 130 feet upgradient of the unlined Cell 1 and may be <br /> affected by dewatering of Cell 1. <br /> ➢ Aites Well: The Aites well is located west of the site on the north side of Weld County Road 24'/4. <br /> This well is approximately 400 feet upgradient of the unlined Cell 1 and may be affected by <br /> dewatering of Cell 1. <br /> ➢ England Well: The England well is located west of the site on the north side of Weld County Road <br /> 24%. This well is approximately 590 feet upgradient of the unlined Cell 1 and may be affected by <br /> dewatering of Cell 1. <br /> ➢ Vogl Well: The Vogl well is located near the intersection of Weld County Roads 11 '/4 and 26. <br /> This well is upgradient of the lined cells 2a and 3 and downgradient of the Last Chance Ditch <br /> (between the Last Chance Ditch and the lined cells). Effects on this well are anticipated to be <br /> minimal. <br />