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Mr. Mark Johnson <br /> October 16, 2017 <br /> Page 2 <br /> reclaimed since at least 1999. The Wildlife Pond was proposed to be left as open water storage but there has been <br /> discussions to reclaim the pond as a slurry lined pond. <br /> Since all ponds are reclaimed except the Wildlife Pond the only potential for slope stability issues arises from the <br /> Wildlife Pond. The mine slopes are 2 horizontal to 1 vertical and shallower in spots. The excavation is <br /> approximately 20 to 25 feet deep. The material onsite is 3 to 4 feet of overburden and 15 to 20 feet of sand and <br /> gravel overlying bedrock. The bedrock is the Denver Claystone formation. The alluvial sand and gravel are <br /> cohesion-less and range from 30 to 40 degree friction angles. The overburden and claystone have friction angles <br /> in the 20 to 30 degree range and typical have cohesions of 200 psf. Groundwater is approximately 5 to 10 feet <br /> below grade. <br /> A slope stability analysis on the "Lee Amendment"adjacent to the site to the north using very similar parameters as <br /> stated above resulted in a minimum setback to surrounding structures of 30-feet at a 2.5 horizontal to 1 vertical <br /> excavation slope. The minimum setback from Weld County Road 13 is 96-feet and is sufficiently spaced away from <br /> the mine highwall and safe for surrounding structures. <br /> CONCLUSIONS <br /> The original La Poudre Mine has been mined out and no further dewatering or mining will occur. The east area has <br /> been mined out for approximately ten years and the west area for approximately two years. The west area(wildlife <br /> lake) is not slurry lined and will be backfilled or slurry lined in the future. The east area has been slurry lined and is <br /> being used by Central Colorado Water Conservancy District. The mining areas are safe to surrounding structures. <br /> LIMITATIONS <br /> Our review is based on regional geologic mapping, present mining plans, public well construction data, and stability <br /> analyses using typical strength parameters for the various strata in the critical sections. Should the mining plans <br /> change or subsurface conditions vary from those portrayed in this letter, we should be contacted in order to re- <br /> evaluate the potential effects on permanent man-made structures. Stability analyses were run at the structure in <br /> question and were not run on failure surfaces closer to the highwall. Note also that surcharge loads due to <br /> temporary material stockpiles and overburden berms were not considered in the analysis as there are no plans to <br /> have berms or stockpiles around the perimeter of the mine. <br /> Please call with any questions or comments. <br /> Sincerely, <br /> Civil Resources, LLC <br /> Andy Rodriguez, P.E. <br /> Civil Engineer <br /> JABestway-2131WinsdoALA POUDRE AMENDMENT1ExhibitslStability Analysis\Stability analysis existing La Poudre mine10-16-17.doc <br />