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Knight Piesold CONSULTING Environmental Department, Meg Burt, Senior Manager October 8, 2018 Cripple Creek and Victor Gold Mining Co. (Newmont) due to the expansion of the Squaw Gulch Valley Leach Facility (VLF) 2. CC&V directed Knight Piesold to reevaluate this EMP based on the reduced area. Once VLF 2 construction activities commence, the existing storage and spillway conveyance capacities of EMP 8c will be sufficient to meet the design criteria. Furthermore, voids (fissures below the ground surface created from historic mining operations and local geology) in the area of EMP 8c could pose a safety hazard during storage capacity expansion efforts. • EMP 9a-d: The impoundment volume and spillways are stated to need upgrades. The four spillways were redesigned. However, the impoundment volume will not need an upgrade because Knight Piesold has designed a new diversion channel, denoted as DC-EMP8a, that will divert runoff from the upper part of the existing contributing area for EMP 9a-d to EMP 8a instead (reference Figures 3.1 and 3.2). This channel will reduce the contributing area to EMP 9a-d such that its existing capacity will be sufficient and will increase the contributing area to EMP 8a, which is more amenable to expansion. • EMP 11: The impoundment volume and spillway are stated to need upgrades. However, CC&V has decided to reclassify this structure as a 'non-EMP' structure because it does not fit the definition or purpose of an 'EMP' at the mine. It is located in a depression above the Arequa Gulch VLF, not at the perimeter of the mining infrastructure. Furthermore, the existing capacity is sufficient to store the runoff volume from a single 10-year/24-hour storm event, and voids in this area could pose a safety hazard during expansion efforts. CC&V will regularly monitor the sediment accumulation within this structure and perform sediment removal efforts as often as necessary to maintain adequate storage for the runoff 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 were presented to CC&V in the design report, 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 were 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 c 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. 9