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Knight Piesold CONSULTING Environmental Department, Meg Burt, Senior Manager April 27, 2018 Cripple Creek and Victor Gold Mining Co. (Newmont) volume associated with a single 10-year/24-hour storm event. Further analyses were not performed for this structure and it is marked as not requiring upgrades, including the impoundment and spillway. The modified EMP and diversion channel basin delineations are presented on Figures 3.1 and 3.2, respectively. The updated analyses for the modified designs, which will be presented to CC&V in the design report once complete, account for modifications to the hydrologic analyses (e.g., contributing areas, CNs, routing parameters, models, etc.) and hydraulic analyses. By way of summary, Table 3.1 presents the design upgrade concepts that will be completed by Knight Piesold. This table can be directly compared to the original evaluation presented in Table 2.9 to identify the changes described in this section. 4.0 EMP 22 DESIGN UPGRADES This section presents the civil design upgrades that were completed for EMP 22. The total impoundment volume was increased to comply with the storage design criterion via the addition of a second impoundment downstream of the existing impoundment. This required the design of two new spillways; one to connect the two impoundments and one to discharge flows to the downstream environment. 4.1 Hydrologic Analyses The hydrologic analyses methodologies and associated input parameters that were used are described in Section 2.3. The results of the analyses to estimate 2x the runoff volume generated from the 10-year/24- hour storm event per the storage design criterion are presented in Table 2.7. The required storage volume for EMP 22 is approximately 37,300 cubic feet(ft3). The HEC-HMS hydrologic model flow routing diagram and peak flow results for the spillways are presented on Figure 4.1 and in Table 4.1, respectively. The following 100-year/24-hour storm event peak flows were estimated: • Inflow to impoundment no. 1: 11.7 cubic feet per second(cfs) • Outflow from impoundment no. 1 to impoundment no. 2(i.e., spillway no. 1): 11.0 cfs • Outflow from impoundment no. 2 to downstream environment(i.e., spillway no. 2): 10.5 cfs The latter two flows were applied as inputs to the hydraulic design analyses, which are presented in the following section. 4.2 Hydraulics Analyses The hydraulic analyses methodologies, associated input parameters, and design criteria that were used are described in Section 2.4. The detailed hydraulic sizing calculation results for the spillways' inlet weirs and outlet channels (i.e., chutes) are presented in Tables 4.2 and 4.3, respectively. The designs are summarized as follows: • Bottom width: 10 feet(both weirs and both chutes) • Side-slopes: 2.0 horizontal to 1.0 vertical (2H:1V, both weirs and both chutes) • Normal flow depths: 0.5-foot(both weirs), 0.3-foot(both chutes) • Freeboard depths: 1.0-foot(both weirs and both chutes) • Channel depths (normal + freeboard depths): 1.5 feet(both weirs), 1.3 feet (both chutes). Note that the chutes were designed with channel depths of 1.5 feet for consistency. • Riprap Dso: 6 inches(both weirs and both chutes) • Riprap placement thickness(2x Dso): 1.0-foot(both weirs and both chutes) • Geotextile: Non-woven 8 ounce-per-square-yard (oz/sy) layer required beneath all riprap placements to provide better long-term stability of the underlying subgrade material. 9