2021-06-08_REVISION - M2001046 (9)

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CIVIL RES'I0URCES Irrigation: The site is located in an area of irrigated cropland. Applied irrigation that is not lost to evaporation and transpiration likely recharges the groundwater. Y Alluvial wells: Other than the eight monitoring wells drilled at the site for monitoring groundwater levels, there are also eight pumping wells permitted within 600 feet of the mine property. There are three wells north of the site, three wells east of the site, one well south of the site and one well west of the site. If pumping, groundwater will be drawn to these wells. Potential Slurry Wall and Mining Impacts to Local Groundwater Levels For all lined cells, a properly constructed slurry wall will tend to isolate these cells from the surrounding alluvial groundwater table. The liner around these cells could cause "mounding" of groundwater (increase in groundwater elevation) on the upgradient side (south and south east) of the lined cells and a potential "shadow effect" (reduction in groundwater level) on the downgradient side (north and northwest) of the mine. Because the liner will tend to isolate thes cells from the surrounding groundwater table, the effects of dewatering when mining lined cells will tend to not extend beyond the liner. Any mounding effect on the upgradient side of the site (south and southwest) is anticipated to be on the order of a few feet or less and will dissipate with distance from the mine. Similarly, shadowing effects will be on the order of a few feet and will dissipate with distance from the mine. The shadowing effects will be minimized by the presence of the Saint Vrain River to the northwest and the Last Chance Ditch that runs between the site and the Varra Pit. Dewatering of the unlined cells (Cells 1 and 2)will result in decreases in water levels around these cells. Since there are no wells permitted within 600' of the unlined cells, the effects of dewatering the unlined cells will be minimal. Area Wells A review of the permitted wells on file with the State Engineer's Office (SEO), Division of Water Resources (DWR) indicates that there are eight permitted pumping wells within 600 feet of the permit boundary. All of these wells are screened in the alluvium. None of these wells are within 600 feet of the unlined cells (Cells 1 and 2) Wells within 600 feet of the permit boundary are discussed below: y Varra Companies Inc Well (Permit#74385-F): Located to the west and downgradient of the slurry wall lined Cell 4. This well may see a groundwater shadow effect from the slurry wall which will be minimized by it's proximity to the lateral of the Last Chance Ditch that runs between the well and the slurry wall y Johnson Well (Permit #219284): Located north and downgradient of the slurry wall lined Cell 4 across State Highway 66. This well may see a groundwater shadow effect from the slurry wall which will be minimized by it's proximity to the lateral of the Last Chance Ditch. r Marquez Well (Permit#152561--A): Located north and downgradient of the slurry wall lined Cell 4 across State Highway 66. This well may see a groundwater shadow effect from the slurry wall which will be minimized by it's proximity to the lateral of the Last Chance Ditch. y Kurtz Estates Well (Permit #152516): Located north and downgradient of the slurry wall lined Cell 4 across State Highway 66. This well may see a groundwater shadow effect from the slurry wall which will be minimized by it's proximity to the lateral of the Last Chance Ditch.