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<br />• saturation of the surficial colluvial soils that theoretic~~lly could <br />occur after an extreme precipitation event, is more critic~il for the <br />stability of the waste piles. It was taken into account for the purpose <br />of the stability analyses described in Section 4.0. <br />3.3 Surface Water <br />3.3.1 Watershed Description <br />The Ralston Creek watershed above the mine site and facilities <br />is mountainous and predominantly forested. The watershed is shown <br />delineated on Plate 3. The total watershed area above the waste rock <br />piles is estimated at 38.3 square miles. <br />Elevations in the Ralston Creek watershed area range from about <br />10,500 feet (mean sea level datum) in the western mountains to approxi- <br />• mately 6,950 feet in the creek bed at the downstream portion of the <br />waste rock piles. The watershed is steep, with the slope of Ralston <br />Creek averaging about 3 percent in the vicinity of the pilE~s. A sum- <br />mary of the measured and estimated watershed characteristics is pre- <br />sented in Table 1. Vegetative and soil cover characteristic~> are also <br />noted in the table. <br />3.3.2 General Climatology <br />The climate in the region is characterized by dry summers and <br />cool winter periods. The mean annual precipitation over tl~e Ralston <br />Creek watershed generally averages about 23 inches (Soil Conservation <br />Service, 1980). About 30 percent of the mean annual precipitation <br />occurs as snowfall. Based upon Soil Conservation Service (SCS) snow <br />course data for the Baltimore Station, located in Sect. 4, T2S, R73W <br />(about 5 miles north-northwest of the Ralston Creek watershed:, Plate 3), <br />the average snow depth on the ground at approximately elevation <br />• <br />- 10 - <br />