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Mr. Nathan D. Phelps, P.E. August 16, 2018 <br /> Page 2 of 5 <br /> In accordance with the letter dated April 30, 2010 from the Colorado Division of Reclamation, <br /> Mining, and Safety ("DRMS"), all sand and gravel mining operators must comply with the <br /> requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the <br /> protection of water resources. The April 30, 2010 letter from DRMS requires that you provide <br /> information to DRMS to demonstrate you can replace long term injurious stream depletions <br /> that result from mining related exposure of groundwater. The DRMS letter identified four <br /> approaches to satisfy this requirement. In accordance with approach nos. 1 and 3, you have <br /> indicated that a bond has been obtained for $175,334 through the DRMS to assure that <br /> depletions from groundwater evaporation do not occur in the unforeseen event, or events, <br /> that would lead to the abandonment of the North River Pit. <br /> DEPLETIONS <br /> Since no mining is planned during 2018, pond evaporation will be the only water demand at <br /> the site. During the past year, portions of the north pond have been backfilled, reducing the <br /> total water surface area. The total water surface area for the two ponds at the site was <br /> measured from the 2017 aerial photograph and was found to be 7.68 acres. For the purposes <br /> of this SWSP, the evaporation from the 7.68 acres was calculated as 30.87 acre-feet/year, <br /> based on a net annual evaporation of 4.02 feet from the Lower Arkansas Water Management <br /> Association's ("LAWMA") decree in Case No. 02CW181. A Glover analysis was used to estimate <br /> the timing of stream depletions with the following parameters: <br /> Transmissivity(T): 142,000 gpd/ft <br /> Specific Yield (S): 0.2 <br /> Distance from centroid of cell <br /> to the river(X): 760 feet (northern cell), 370 feet (southern cell) <br /> Aquifer Width (W): 5,455 feet <br /> According to the Glover analysis, 95 percent of depletions were modeled to accrue to the <br /> stream within the first 8 months; therefore, an 8 month unit response function will be used to <br /> calculate lagged depletions for the purposes of this SWSP, as shown below: <br /> Unit Response Function <br /> Month Month 2 Month 3 Month 4 Month 5 Month 6 Month 7 Month 8 <br /> 1 <br /> Northern 0.6185 0.2108 0.0569 0.0351 0.0276 0.0209 0.0170 0.0132 <br /> Cell <br /> Southern 0.8260 0.1183 0.0267 0.0163 0.0127 <br /> Cell <br /> Since 95%of the depletions occurred within the first eight months for the northern cell and <br /> the first 5 months for the southern cell, the last 5%of the lagging factors were wrapped. <br /> The lagged stream depletions are calculated as 29.89 acre-feet/year (column 10 of attached <br /> Table 1). The carry-over lagged depletion associated with the surface area during the <br />