2011-11-15_REVISION - M1980055HR

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• 12.3 Mean Monthly Temperatures and Ranges C: \Documents an Settings \cwoodwerd.DMC \Desktop \Environmental Protection Plan Sunday Mines Revised November 2011 revl (2) 11 10 11.docx Section 12 Climate Table 12 -3 shows the monthly average maximum and minimum temperatures for the period of record. Large daily temperature fluctuations are typical for this semi -arid to arid region, with upwards of 30° Fahrenheit (F) to 40° F fluctuations between night and day during most of the year. Summer high temperatures can reach 100 °F or greater and winter low temperatures can reach below 0° F, however, daytime highs in the winter are normally above freezing (32° F). 12.4 Evaporation Rates Pan evaporation data are not available at the Uravan station. Therefore, pan evaporation data were collected from a monitoring station at Dead Horse Creek near Naturita, Colorado. The period of record for these data extends from 1971 to 1980. Table 12 -4 shows the pan evaporation data from the monitoring station at Dead Horse Creek near Naturita, Colorado. Figure 12 -4 illustrates the relationship between average monthly precipitation measured in Uravan and average monthly pan evaporation from the Dead Horse Creek monitoring station data. This figure shows that monthly pan evaporation is greater than monthly precipitation from April through October. During the late fall to early spring months (November through March), pan evaporation is not measured due to regular freezing temperatures at night and daily thaw. Actual evaporation is likely to be less than pan evaporation due to affects such as available soil moisture, infiltration into the subsurface, variations in surface topography, and differences related to the effect of the evaporation pan on measured evaporation rates. Pan evaporation exceeds precipitation by approximately 4 times based on the available data. 12 -2