2019-06-28_REVISION - M1977004 (12)

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Homestake Mining Company May 10,2019 Regular(112d)Operation Reclamation Permit Application Package 1.0 INTRODUCTION Pitch Mine is owned and operated by Homestake Mining Company (HMC) as a subsidiary of Barrick Gold Corporation. The Pitch Mine is located in the Sawatch Range of Saguache County, Colorado within the Gunnison National Forest. Open pit mining operations ceased in 1984 following a pit wall failure on the east side (East Wall) of the North Pit in October of 1983. The facility has been undertaking reclamation and closure activities since that time and is currently referred to as the Pitch Reclamation Project (Project). This Project Memorandum provides an overview of past climate data for the Project reported back several decades ago and a review of data available through 2018 for any significant differences. 2.0 CLIMATE OVERVIEW The climate within the region of Colorado encompassing the Project is semi-arid. From interpolated information based on records from the site and a location six miles west of Sargents, Colorado, an average of approximately 16 to 20 inches of total precipitation falls annually on the Project area. A significant percentage of precipitation occurs as snowfall (Golder, 1994). Most snowmelt runoff occurs in May and early June. Historic peak discharges are the result of thunderstorms which occur during the summer months. Because the Project area watershed is small, potential thunderstorm generated flood peaks exceed the potential snowmelt flood peaks (Golder, 1994). 2.1. Climate Data from Previous Reports Past data from Golder (1994) utilized NOAA Atlas 2, Volume III, published by the United States Department of Commerce and determined precipitation depths for various recurrence intervals as shown in Table 2-1. This data shows the 200 year, 24 hour event to be 3.2 inches. BGC reviewed the most recent storm event data for the site (NOAA, 2019)and interpolated a 200 year, 24 hour storm event to be 3.36 inches. As the 2019 value is within 5% of the 2014 value, the hydrology should not be re-analyzed for the site, but any new channel hydrology calculations should use the 2019 value. Precipitation amounts were recorded at the project site between 1983 and 1990. During the eight- year period, average annual precipitation was 16.9 inches, with a maximum of 22.9 inches and a minimum of 12.8 inches. Monthly precipitation amounts rarely exceeded three inches, although a peak monthly rainfall of 7.2 inches was recorded in August 1984 (Golder, 1994). 2.2. Updated Climate Data New climate data are summarized from NOAA(2019)for Table 2-1. Values were taken from both the project site (location selected over the pit) as well as nearby stations (Appendix A). From the interpolated values by NOAA(2019)for the Project site, the 24-hour storm 50-year, 200-year, and EXHIBIT K-RULE 6.4.11 (CLIMATE INFORMATION) Page 1 HOMESTAKE MINING COMPANY