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Knight Piesold CONSULTING Environmental Department, Meg Burt, Senior Manager October 8, 2018 Cripple Creek and Victor Gold Mining Co. (Newmont) - Reservoir surface area at"high-water line"greater than 20 acres(ac) - Dam height"measured vertically from the elevation of the lowest point of the natural surface of the ground where that point occurs along the longitudinal centerline of the dam up to the crest of the emergency spillway of the dam"greater than 10 feet • Rule 4.2.5.2, "Non jurisdictional Size Dam" - Reservoir capacity less than or equal to 100 ac-ft - Reservoir surface area at"high-water line" less than or equal to 20 ac - Dam height less than or equal to 10 feet Based on the pre-mine development and as-built EMP topography contours provided by CC&V, Table 2.10 summarizes the Jurisdictional Dam status for each EMP. The results indicate that eleven of the EMPs are non-Jurisdictional Dams and six are currently estimated to be Jurisdictional Dams. The six Jurisdictional Dams are classified as such based on dam height alone; the reservoir capacities and "high-water line" surface areas are within the non-Jurisdictional Dam criteria. The upgraded designs produced by Knight Piesold include lowering the spillway inlet invert elevations for the EMPs that are currently classified as Jurisdictional Dams. Once the upgrades are constructed, these EMPs will become non-Jurisdictional Dams. 2.5.3 Comparisons to Previous Estimates This section presents comparisons of key parameters between estimates made by Steffens and Knight Piesold. Information from the Steffens (2012) document is compared to the information presented by Knight Piesold herein. The Steffens (2012) design report used a 10-year/24-hour (10-yr/24-hr) storm event with a depth of 2.7 inches, and a 100-yr/24-hr storm event of 3.5 inches. The storm events used in the Steffens report were sourced from the NOAA Atlas 2 Volume 3, which was last revised in 1973. More recent analyses have been performed in the NOAA Atlas 14 Volume 8, which supersedes the NOAA Atlas 2 Volume 3. NOAA Atlas 14 Volume 8 used increased data quality control and a longer period of record and reported a 10-yr/24-hr storm event depth of 2.4 inches and a 100-yr/24-hr storm event depth of 4.1 inches for the Cripple Creek station near the mine site. Knight Piesold was able to independently corroborate the storm depths using the records from the Cripple Creek Station, as well as with data from the on-site weather stations. Comparisons of contributing basin areas and runoff CNs are presented in Table 2.8. There are some significant discrepancies in the basin areas to the EMPs. The following potential justifications were made, which were largely confirmed by CC&V: • EMP 8a: Knight Piesold estimated a smaller area because the previous inflow diversion channel that Steffens considered was removed. • EMPs 9a-d (combined): Knight Piesold estimated a larger area because a new inflow diversion channel was constructed that Steffens did not consider. • EMP 13: Knight Piesold estimated a larger area because Steffens did not include the area up-gradient of the road within the catchment. • EMPs 16, 17, and 20: Knight Piesold estimated smaller areas because Steffens included the ECOSA waste rock area to these EMPs. CC&V directed Knight Piesold to assume runoff from the waste rock area will be detained by the toe berm. To this end, Knight Piesold estimated the required size (volume) of the toe berm herein. • EMP 21: Knight Piesold estimated a smaller area but a robust justification for the larger Steffens area could not be found. This could be simply due to differences in topography.