2010-05-07_REVISION - M1977493 (10)

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Permit Amendment (AM-06) - Climax Mine • K-1 Introduction The elevation of the Climax Mine site varies from about 10,230 ft amsl near the toe of 5 Dam to nearly 13,850 ft amsl on the peaks surrounding the open pit. Therefore, the climate is typical of high-elevations in the Rocky Mountains. The climate is generally characterized by cool summers with a short growing season and extremely cold winters. During July, which is typically the warmest month, the average daily high and low temperatures are about 65°F and 39°F, respectively. During January, which is typically the coldest month, the average daily high and low temperatures are about 25°F and 2°F, respectively. On average, the Climax site receives about 23 inches of precipitation, of which, about 80 to 90 percent falls as snow. The Climax Mine is fortunate, and perhaps unique among high-elevation mine sites, in that it has a relatively long record of reliable climate data. Climate and weather information has been recorded on-site at the Climax Weather Station since the 1950's and at the Fremont Pass SNOTEL site (formerly Snow Course) since the 1930's. K-2 Climax Weather Station The Climax Weather Station is located to the west of Highway 91 near the top of Fremont Pass, at a latitude of 39.37°, a longitude of 106.18°, and at an elevation of 11,294 ft amsl. Precipitation and temperature data at this station are recorded daily by Climax personnel and reported to the National Oceanic and Atmospheric Administration (NOAA) for publication through the National Climatic Data Center (NCDC). Those data are available through NOAA's monthly Climatologic Data publications. In addition, daily data from the Climax Weather Station are available at http://cdss.state.co.us/, which is maintained by the Colorado Division of Water Resources. These sources provide daily data and monthly summaries nearly continuously for the period from 1952 through 2006. Some data are also available for the period from 1949 through 1952. However, those data are sporadic and therefore not included in the period of record presented herein. The temperature and precipitation data from the Climax Weather Station are summarized in Tables K-1 through K- 4 and shown on Figures AM-06-K-01 though AM-06-K-04. K-3 Fremont Pass SNOTEL Station The Fremont Pass SNOTEL station is located on the north slope of Chalk Mountain, at a latitude of 39.38°, a longitude of 106.20°, and an elevation of 11,400 ft amsl. The station began measuring snowfall, snowpack, and snow water equivalent (SWE) as part of the National Resources Conservation Services (NRCS) snow telemetry (SNOTEL) program in 1981. Measurements of the accumulated snowpack and SWE are taken daily by a pressure-sensing snow pillow. Precipitation and temperature data are also available; however, given the longer period of record, data from the Climax Weather Station has traditionally been used to represent the Climax site. Since 1939, monthly snowpack readings have also been recorded for the Fremont Pass Snow Course site, which was located near the current SNOTEL site. The overlapping period of record for the two sites was used to develop a correlation to assimilate monthly snowpack values for the SNOTEL site back to 1939, thus creating a longer period of record. The assimilated data, however, does not necessarily indicate the actual peak snowfall for each year unless the peak happened to occur on about the same day as the Snow Course reading. Snowpack data from the Fremont Pass SNOTEL and Snow Course sites are summarized in Table K-5 and shown on Figure AM-06-K-05. K-4 Design Rainfall Events Design rainfall depth-duration data for various return periods ranging from 2 to 1,000 years have been estimated from NOAA Atlas 2 as well as through a Log Pearson Type III statistical analysis of the historical daily precipitation data. These two approaches provide considerably differing results. Results from both analyses have been included herein for completeness and it should be the users discretion as to which set of storms is most appropriate for the intended use. The 24-hour rainfall depths from both design rainfall analyses are provided in the Table K-6. • The Log Pearson Type III analysis is based on 55 years of available daily precipitation data. Although this methodology provides estimates for storms with longer return periods, the storms with return periods greater Exhibit K K-1 May 2010