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12.0 Climate <br />. The Van 4 Mine is located within an and environment. Climatic conditions in this <br />area generally include moderate to cold winter night time temperatures with hot <br />summer daytime temperatures, large daily temperature fluctuations typical of and <br />climates, and a large excess of evaporation over precipitation. <br />12.1 Annual Precipitation <br />Weir et al (1983) investigated climatic fluctuations within the Dolores River Basin, and <br />observed that precipitation is correlated with elevation, with highest precipitation <br />amounts occurring within mountain areas surrounding the basin, and markedly <br />lower precipitation occurring within the central lower-elevation basins. Site-specific <br />climatic data are not available for the Van 4 Mine. Therefore, temperature and <br />precipitation data were collected from the Uravan, Colorado, National Oceanic <br />Atmospheric Administration (NOAA) weather station. Precipitation at Uravan is <br />estimated to be similar to the mine area based on an ischyetal map provided by Weir <br />et al. (1983). The period of record for this weather station extends from 1961 through <br />2007. <br />Table 12-1 shows the monthly total precipitation data for the period of record and <br />Figure 12-1 is a box plot showing monthly total precipitation summary statistics. <br />October, August, and September are the wettest months of the year, with median <br />monthly precipitation totals of 1.36 inches (in), 1.25 in, and 1.04 in., respectively. June, <br />February, December, and January are the driest months of year, with median monthly <br />precipitation totals of 0.34 in, 0.61 in, 0.64 in, and 0.70 in, respectively. The wettest <br />month on record is October 1972 when 5.89 in of precipitation were recorded at the <br />Uravan station. <br />Figure 12-2 compares the annual precipitation to the average annual precipitation <br />over the period of record, which shows extended periods of particularly high or low <br />precipitation. This data is shown in terms of water year totals, from October through <br />September. The average annual precipitation for water years 1962 through 2007 is 12.6 <br />in. Note a yearly total for water year 1961 could not be computed because <br />precipitation data from October through December of 1960 are not available. <br />Maximum annual precipitation was recorded in 1997 at 19.87 in, while the minimum <br />precipitation was recorded in 1974 at 7.66 in. <br />12.2 Direction and Velocity of Prevailing Winds <br />Data regarding wind speed and direction are presented in Table 12-2 and Figure 12-3. <br />12.3 Mean Monthly Temperatures and Ranges <br />Table 12-3 shows the monthly average maximum and minimum temperatures for the <br />period of record. Large daily temperature fluctuations are typical for this semi-arid to <br />and region, with upwards of 30° Fahrenheit (F) to 40° F fluctuations between night <br />and day during most of the year. Summer high temperatures can reach 100°F or <br />greater and winter low temperatures can reach below 0° F, however, daytime highs in <br />the winter are normally above freezing (32° F). <br />12-1 <br />T:\64986-Denison Mines\Task Order 4 - EPP Sunday Mines Group_Van4\Van4\FINAL Report\FINAL - Environmental Protection Plan Van4.doc