2017-03-27_REVISION - M1981185 (27)

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The portal of the Idaho No. 1 mine is situated at approximately 8,792 feet above mean sea level (AMSL). The portal of the May Day Mine No. 1 is located approximately 9,235 feet AMSL. 5.0 CLIMATOLOGY The May Day Idaho Mine Complex is located in the Little Deadwood Gulch drainage of San Juan National Forest (sub basin 14680105). The climate in this portion of the central Rocky Mountains in southwestern Colorado can be variable with notable differences in microclimate due to slope, aspect, and elevation. Elevations on the site range from 8,600 feet (AMSL) along the La Plata River floodplain to approximately 9,600'. Typical mid-summer afternoon temperatures are in the upper 70 degrees Fahrenheit(F°), with nighttime around 400171. Conversely, the wintertime high temperatures are around 40°F, with nighttime in the low 10°F (Figure 3). In general, since temperatures decrease with elevation with mountainous terrain,the lower portion of the site may be warmer than the higher locations. Summer afternoon temperatures can decrease about 4 to 50F per thousand feet in elevation. The average annual precipitation for this area is 18.0". This tends to be received throughout the year with most months receiving at or greater than 1" of rain or water equivalent as snow(Figure 4). Late summer through early fall receives the most moisture with July and December typically getting over 2 inches. On average, rainfall is lightest in midsummer, with June being the driest month. Deviations from these averages are high both within months and between years. In summer, Baldy Peak and the surrounding ranges are effective thunderstorm generators whenever the regional air masses are sufficiently moist. The last half of July and much of December are particularly prone to mountain thunderstorms. Snow and soft hail are possible from mountain storms even in July and December. Winter precipitation generally falls as snow from October through April. The mean annual snowfall for this area over the last 50 years has been 80" with over 15"per month falling between December and February (Figure 5). A portion of this snow melts during the warmer days; however, some snow accumulates without melting during midwinter,particularly in north- facing, shaded and level areas. This accumulation and melt results in an average on ground snow depth of 12 to 15"during January and February. The remainder of the snow melts during May and June resulting in water run-off. 1 All climate data is from the Fort Lewis weather station as reported by the High Plains Regional Climate Center: http://www.hprcc.uni.edu/c�4i-bin/cli perl lib/cIiMAIN.pl?co3016 available July 16,2010. May Day Idaho Mine Complex M-1981-185 January 19, 2017 Page I -6-