2019-06-28_REVISION - M1977004 (12)

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Homestake Mining Company May 10,2019 Regular(112d)Operation Reclamation Permit Application Package forest coverage is estimated to exceed 70 percent east of the mine property, and to be approximately 50 percent forest cover to the west of the mine. During the time the Golder report was being written (Golder, 1994), another organization (SCS) was currently undertaking a soil survey for the area, but the work had not been published. Portions of the unpublished draft were obtained by Golder, and several soil series were identified by the SCS for the area encompassing the Pitch Mine. Undisturbed areas are covered by Engelmann Spruce-Subalpine Fir, and Lodgepole Pine. Soils include the Peedee, Ohman, and Losee series, with the Seitz series identified for the rock out crop areas. The Hydrologic Soil Group applicable to these soil series is generally `B', with some `A' and 'C' groups identified. These are generally free draining soils, with relatively high infiltration rates; stormwater runoff is therefore reduced. The rock outcrop areas have been classified as group 'C' and `D' soils, which produce significantly more runoff. This information was utilized in determining the amount of rainfall that becomes runoff for determining stormwater discharges (Golder, 1994). Review of historical aerial photography in 2019 indicates the overall types and distribution of vegetation has remained relatively consistent over the past several decades. Therefore, it is expected that on average, infiltration and runoff characteristics at the Project site are still similar. 2.4. Conclusion Pitch Mine is a uranium mine located in Saguache County, Colorado currently undertaking reclamation and closure activities. The site is semi-arid and averages approximately 16 to 22 inches total precipitation annually. Most snowmelt runoff occurs in May and early June, but historic peak discharges are the result of thunderstorms which occur during the summer months. Precipitation depths for 24-hour reoccurrence intervals were provided back in 1994 and are similar to current data. Historic precipitation data from 1958 to 2018 were used to also compute monthly maximum, minimum, and average values. Surface characteristics, primarily in the form of vegetation, have remained relatively unchanged since 1994 and unlikely to lead in any significant overall changes in infiltration and runoff characteristics. Based on this analysis, the precipitation data from Appendix A should be used as the design storms for new facilities at the Pitch site. These values will not produce results that are materially different from the previously used values, but they do incorporate the data from 1994 to 2019 and therefore represent the most complete data set at this time. EXHIBIT K-RULE 6.4.11 (CLIMATE INFORMATION) Page 4 HOMESTAKE MINING COMPANY