2012-01-06_PERMIT FILE - C1982057 (27)

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Seneca Mine valley from the Yampa River valley, they are forced to the south or • up valley, resulting in winds from the north-northwest. This explains how prevailing upper level west or south-west synoptic winds become northerly at the surface in the Seneca Mine val~l ey, Thus, the winds on a typical day at the Seneca Mine site are controlled by two factors, the extent to which the cool air layer builds during the night, and the intensity of the synoptic wind fields. As the night progresses, the drainage winds from the south develop unless the synoptic winds are strong enough to counteract the cooling effects. The valley drainage winds will persist until after sunrise when the valley surface begins to heat. In the summer, the drainage flow will break down sooner than in the winter due to the more direct angle of the sunlight and greater amount of surface heating. It is possible in the winter to never heat up enough to break the diurnal temperature inversion, resulting in light variable winds throughout the day which would otherwise have been stronger and relatively constant as the valley winds linked up with the synoptic regime. In the summer, the synoptic weather patterns are much weaker than during the winter, allowing the surface of the valley and the valley air to • heat up considerably. This hot air is bouyant and rises, frequently resulting in up valley flow from the north. This is analogous to the nighttime drainage flow, but has more variability in the winds since the rising air may go up the valley sides rather than being restricted to only down valley flow. The duration and intensity of the unstable convective activity is controlled by the amount of heating required to break the inversion in the morning, Usually by 1800 MST, the sun angle becomes too low to continue heating and by sunset, the stable drainage winds start tc form". The meteorological station at the proposed Seneca II-W Mine area was located in the south one-half of Section 16, TSN, R88W, about 500-600 feet east of Hubberson Gulch (see Figure 8-1). Elevation at the site is approximately 6,850 feet MSL with sensor height at 33 feet AGL. Table 8-3 presents site-specific wind direction data from October, 1980 through September, 1987 (seven complete years), The w3 nds trend from east-southeast to west-northwest which conforms with the general topography of the area. Down valley flow (occurrences from the • east-southeast) accounted for 23.2 percent of the recorded hourly averages. Up valley 6