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<br />determined distance. The depth of the old tailings averages <br />• 10 feet. <br />There are two wooden decant chimnies in the old pond. These <br />are identified as X4 and XS on Plate I. Both discharge into <br />the area south of the old pond and both are partially <br />collapsed. <br />A geotechnical investigation and a subsequent design study <br />addressing the expansion of both ponds were completed by <br />Sutherland, Ricketts and Rindahl of Oenver, CO in late 1980. <br />The investigation included the drilling of 13 test holes of <br />the dike of the new pond and the construction of 9 monitor <br />wells in the area surrounding both ponds. Three of these <br />monitor wells were subsequently damaged at the surface and <br />are no longer useable. <br />The dikes of the old pond were constructed of deslimed <br />tailings sands by the down stream method. The dikes of the <br />new pond were apparently constructed by raising berms of <br />alluvium using earthmoving equipment. This alluvium consists <br />of a mi>;ture of old tailings, talus and gravel. <br />An interceptor drain was under construction during the field <br />work phase of the project. This drain intercepts ground <br />water flows at the east side of the new pond and diverts <br />• them to a ditch north of the pond. The initial portion of <br />this drain passes under the pond. <br />SITE GEOLOGY <br />The tailings ponds abut stream terrace deposits on the east <br />side of the valley which then give way to talus and <br />outcrops of intermediate flows and tuffs of the Silverton <br />Series. The Animas River flood plain lies immediately west <br />of the ponds. In the immediate vicinty of the ponds, the <br />Animas River flows along the northwest side of the valley <br />with bedrock being exposed at numerous locations on the <br />northwest shoreline. <br />Subsurface lithologies have been determined from 22 borings <br />completed in 1980 and 19 completed during the course of the <br />current project. Soil types in the vicinity of the ponds <br />consist of silty sands and gravels of unknown thickness and <br />discontinuous clay lenses. The terrace deposits east and <br />south of the pond contain continuous zones of gravel in <br />excess of 60 feet thick. However, under the pond itself, the <br />gravel occurs as discontinuous, intercalated lenses of <br />variable thicknesses within a thicl: sequence of sand, silty <br />sands and clays. West of the pond, the flood plain deposits <br />• -4- <br />