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eh <br />ESPEY, HUSTON & ASSOCIATES, INC. <br />• <br />utilizing standazd 734-minute USGS topographic maps of the Ninemile Gap and <br />Rattlesnake Mesa quadrangles. Preparation of the map consisted of visually <br />identifying azeas of uniform slope and then measuring the slope of those azeas. The <br />slope gradient was measured by counting surface elevation contours (40-foot <br />intervals) in 3i-inch (500-foot) intervals. For example, two contours in 3: inch equals <br />80 feet per 500, which equals 16 percent slope. Slopes throughout the azea were <br />then classified into the following slope classes: 0-6 percent, 7-14 percent, 15-30 <br />percent, 31-50 percent and greater than 50 percent. A similar procedure using 100- <br />foot horizontal intervals was used to construct Exhibit F-2. <br />Ground slopes within the mine plan area are controlled principally by the <br />trellis drainage patterns of Curtis Creek and Aicher's Draw. The flatter and steeper <br />terrain within the permit azea is closely associated with these drainages. The areas <br />of steepest gradient tend to occur along the slopes adjacent to Curtis Creek, <br />• Aicher's Draw and generally in the southern portion of the mine plan azea. Where <br />deeply incised along its 1.47-mile stream course, the water gap occupied by Curtis <br />Creek ranges from 200 to 800 feet and is about 200 feet wide in the valley floor. <br />The gradient of Curtis Creek is 0 to 6 percent for the approximately 3 miles within <br />the mine plan area. <br />The eastern portion of the mine plan azea, drained by Aicher's Draw, <br />includes approximately 1,061 acres (2Z percent) of the total land surface. Slope <br />gradients along the course of Aicher's Draw vazy from less than 6 percent at the <br />head of the valley to greater than 50 percent in the south where it leaves the area <br />of interest. No surface disturbance will take place within the drainage area of <br />Aicher's Draw. <br /> <br />F-2 <br />