1991-09-20_HYDROLOGY - M1977378 - Laserfiche WebLink

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San Juan County Mining Venture Job No. 3121K073 The southwest side of the pond, at the base of the steep slope is bound by Boulder Creek. The south base of the pond is bound by an existing gravel road. The north side of the pond abuts against the mountain to the north. The Animas River is located several hundred feet southeast of the existing pond. SITE CONDITIONS The exterior surface of the tailings pond and the top of the east side primarily consists of sands, and the interior at the surface on the west side consists of clayey silts or slimes . The southwest side of the pond overflowed in 1977 during operation and wasted a large volume of sands and slimes into Boulder Creek. A dike consisting of sandy clay and gravel has been constructed across the past failure area to control runoff during precipitation. Tailings placement into Pond 1 has been discontinued since the overflow and washout. When constructed, the tailings were placed by an upstream deposition method. Tailing was discharged hydraulically at the outside crest of the pond and allowed to flow toward the rear. With this method, gravity was used to create a deposition change in gradation of the tailings from the front to rear of the pond. The coarse grained, or sand fraction of tailings settled out first at the front exterior perimeter, while the clay or silt sized (slime) fraction was carried hydraulically to the rear. As the height of the pond was raised, portions of the sand fraction were successively placed over the slimes . Pond water, from the hydraulic deposition, was decanted off of the pond. At the time of our field exploration the surface of the pond was dry. At the time of the monitor well readings, water was located behind the dike at the old failure area. Boulder Creek was flowing at the time of our field exploration, and discharges to the Animals River to the south. -2-