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Nathan Phelps April 10, 2020 Page 2 of 5 that result from mining related exposure of groundwater. The DRMS letter identified four approaches to satisfy this requirement. In accordance with approach nos. 1 and 3, you have indicated that a bond has been obtained for $175,334 through the DRMS to assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, that would lead to the abandonment of the North River Pit. DEPLETIONS Since no mining is planned during 2020, pond evaporation will be the only water demand at the site. The total water surface area for the two ponds at the site was measured from the 2019 aerial photograph (Figure 2, attached) and was found to be 7.42 acres. For the purposes of this SWSP, the evaporation from the 7.42 acres was calculated as 29.83 acre-feet/year, based on a net annual evaporation of 4.02 feet from the Lower Arkansas Water Management Association's ("LAWMA") decree in Case No. 02CW181. A Glover analysis was used to estimate the timing of stream depletions with the following parameters: Transmissivity (T): 142,000 gpd/ft Specific Yield (S): 0.2 Distance from centroid of cell to the river (X): 760 feet (northern cell) 370 feet (southern cell) Aquifer Width (W): 5,455 feet According to the Glover analysis, 95 percent of depletions were modeled to accrue to the stream within the first 8 months; therefore, an 8 month unit response function will be used to calculate lagged depletions for the purposes of this SWSP, as shown below: Unit Response Function Month 1 Month 2 Month 3 Month 4 Month 5 Month 6 Month 7 Month 8 Northern Cell 0.6185 0.2108 0.0569 0.0351 0.0276 0.0209 0.0170 0.0132 Southern Cell 0.8260 0.1183 0.0267 0.0163 0.0127 Since 95% of the depletions occurred within the first eight months for the northern cell and the first 5 months for the southern cell, the last 5% of the lagging factors were wrapped. The lagged stream depletions are calculated as 28.76 acre-feet/year (column 10 of attached Table 1). The carry-over lagged depletion associated with the surface area during the previous plan year was calculated separately as 1.11 acre-feet and then added to the lagged depletions for the current plan year. The resulting total stream depletion associated with the gravel pit is estimated to total 29.87 acre-feet (column 12 of attached Table 1).