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West Elk Mine <br /> <br /> <br />2.04-119 Rev. 08/94- TR71, 06/95- PR06, 03/06- PR10;05/22- MR462 <br />Parameter Site 1 Percent Recovery <br />Site 2 <br />Site 3 <br />Wind Speed 70.77 52.97 79.12 <br />Wind Direction 70.49 52.97 79.33 <br />Ambient Air <br />Temperature <br />68.75 51.65 75.25 <br />Relative Humidity --- 43.93 --- <br />Precipitation --- 53.12 --- <br />Wind <br /> <br />Data collected during the spring and summer quarters of 1977 indicated winds varied at the three <br />sites. Minimum wind speeds ranged from 0.6 mph to 1.4 mph. Maximum wind speeds ranged from <br />12.4 mpg to 19.7 mph. Mean wind speeds at the three sites were between 5.9 mph and 8.3 mph. <br /> <br />Hourly wind speed data showed a consistent daily pattern that was almost identical for Sites 1 and <br />2. The wind speed typically increased during the nighttime hours from about 7:00 p.m. Mountain <br />Standard Time (MST), reaching a peak speed of about 10.5 mph at about 7:00 a.m. the next <br />morning. The average wind speed dropped over two or three hours to reach a morning minimum <br />speed of about 6.0 mph. It then rapidly increased to a second maximum of about 9.5 mph by noon, <br />with a subsequent slow decrease to reach a late afternoon minimum of about 5.0 mph. <br /> <br />The average diurnal variation in wind speed at Site 3 was strikingly different from that at Sites 1 <br />and 2. At Site 3, wind speed remained relatively calm throughout the nighttime hours. Starting at <br />about 8:00 a.m., wind speed increased to about 8.0 mph by 11:00 a.m. It stayed at this level until <br />about 3:00 p.m. when it began to decrease to its relatively constant nighttime level. Although the <br />general shape of the diurnal wind speed curve at Site 3 was markedly different from those for Sites <br />1 and 2, there was a slight hint of an early morning (6:00 a.m.) relative maximum and a morning <br />(8:00 a.m.) relative minimum. However, this behavior was much less predominant than at Sites 1 <br />and 2. <br /> <br />The explanation of this variation is the existence of a well-established drainage flow down the <br />canyon from east to west. A relatively large basin to the east of the area (headwaters of the North <br />Fork of the Gunnison River) provided the volume of air to support this relatively intense flow <br />which was funneled through the narrow canyon past the West Elk Mine site monitoring network. <br />This drainage flow was almost directly opposed to the geotropic or gradient flow which is typically <br />from the southwest. At sunrise, atmospheric heating reduces the horizontal pressure gradient which <br />supports the drainage flow. The wind speed at Sites 1 and 2 dropped to relative minimum within <br />several hours under this influence. Above this low altitude, high speed drainage layer, the winds at <br />Site 3 remained relatively calm throughout the night and well into the morning hours. As discussed <br />later these relatively calm winds were less intense drainage winds themselves. <br /> <br />The pronounced rise in the average wind speed at all sites during the late morning hours was <br />primarily due to the breakup of the surface-based inversion, or stable air, within the valley. As the <br />surface-based inversion was destroyed by solar heating, more vertical mixing of the air which was