2010-08-02_REVISION - M1977300 (37)

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Environmental Protection Plan, Schwartzwalder Mine 13-1 • 13. CLIMATE The Schwartzwalder Mine area has a semiarid climate characteristic of much of the central Rocky Mountain region. Precipitation records from 1978 to 2010 at Ralston Reservoir (located about 2 miles from the site and 560 feet lower in elevation) show a mean annual precipitation of 18.65 inches (Table 13-1). Approximately 40 percent of the precipitation falls during the spring, much of it as wet snow. Thunderstorms (June to August) account for an additional 30 percent of the annual precipitation. Fall and winter are drier seasons, accounting for 20 and 10 percent of the annual precipitation, respectively. Snowfall averages 69.2 inches per year, falling from late September through May. Precipitation variation from the monthly and annual averages is shown in Table 13-2. Based on a standard deviation of 3.68 inches, precipitation ranged from 14.75 to 22.11 inches during 68% of all years. The lowest recorded precipitation was 11.9 inches in 2002 while the highest recorded precipitation was 26.4 inches in 1999. Temperatures at the site are moderate. Extremely warm or cold weather is usually of short duration. Daily summer temperatures ranges from 53 to 88 °F, and winter temperatures range from 23 to 46 °F, on average. Table 13-1. Monthly Climate Summary at Ralston Reservoir May 1, 1978 - December 31, 2009 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov ; Dec Annual Average Max. 45 46 52 59 70 79 88 83 75 62 53 43 62.9 Temperature (F) P ....................................................... ............................................................... ............................................................................. ............................................................................................. _........ .......... ........................... ................... ................... ................ ................ Average Min. • 23 23 29 35 45 53 61 58 50 39 30 22 38.9 TemPerature (F) ....................................................... ............................................................... ....................... .... ........... ......... .................... .......................................... .................. ................... .................. ................................... Average Total 0.6 0.7 1.8 2.5 2.9 2 1.6 2.1 1.4 1.3 1.1 0.8 18.65 Preci itation (in.) ......... .............P................. ..... ............. ... .................................,............................, ............................................................,........................... ....:..... .....;..... Average Total 8.6 8.4 13 10 1.7 0 0 0 0.7 3.7 11 12 69.2 SnowFall (in.) ..................................................................................... ....................................;............................ ............................................... ....................................... ....;.... . _.__.................... Average Snow 1 1 1 1 0 0 0 0 0 0 1 2 1 Depth (in.) Source: Western Regional Climate Center (WRCC), data download for station 056816 (Ralston Reservoir, Colorado), July 31, 2010 Percent of possible observations for period of record: Max. Temp.: 17.1% Min. Temp.: 17% Precipitation: 99% Snowfall: 98.9% Snow Depth: 98.7%. Climate data presented in this section were obtained from the Western Regional Climate Center for the nearest weather station (Ralston Reservoir). Although wind data are not available at the Ralston Reservoir weather station, a weather station operated on the mine site located in Ralston Creek Canyon, approximately 200 feet from the water supply well and slightly east of the water treatment plant. The available data from the mine weather station includes limited wind data from the years 1987 and 1996- 1997. During 1987, the daily wind speed average was 12.1 mph while in 1996, the daily wind speed average was noticeably lower at 8.3 mph (Table 13-3). A wind showing wind speed and direction data in 1997 is shown in Figure 13-1. The limited wind data from this weather station indicate that wind direction and speed both occur most frequently from the northwest. • 4109C.100731 Whetstone Associates •