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Buildo.¢ Mine Tai(in¢s Ponds Evaluation <br />2.0 SITE HISTORY <br />The recent site history for the Bulldog Mine is outlined in the summary of remediation activities <br />and ground water monitoring at the Lower Tailings Pond by P.M. De Dycker & Associates <br />(1996). The discussion that follows is based lazgely on that summary. <br />2.1 Tailings Pond Operation <br />Homestake operated the mill at the Bulldog Mine from the late 1960s until 1985 for the recovery <br />of silver from ore produced from underground mining operations. The locations of the Upper <br />and Lower Tailings Ponds aze shown on Figure 2.1. <br />The mill was initially operated as a flotation process facility for concentration of sulfide ores <br />from the late 1960s until 1978, and [hen as a cyanide ]each process facility from 1978 to 1985. <br />From the late 1960's until 1974, the coazse fraction of mill tailings were discharged into the <br />underground workings periodically, as needed. for mine backfill. During this period, both the <br />fine fraction and total tailings product were dischazged into the Upper Tailings Pond. The total <br />tailings product was dischazged into the Lower Tailings Pond from 1974 to 1985. Both tailings <br />ponds were constructed by spigotting tailings within a valley impoundment formed by an earth <br />embankment constructed across the valley. Tailings fluids were contained by the embankment <br />materials and site subsoils and bedrock. There are indications that some of the older notation <br />mill tailings were dredged from the Upper Tailings Pond and reprocessed in the mill with the <br />cyanide circuit, with subsequent re-disposal in the ponds. <br />2.2 Remedial Activities <br />Starting in 1978, Homestake constructed several features to intercept and collect seepage that <br />was migrating from the Lower Tailings Pond. The Lower Tailings Pond embankment was <br />constructed as across-valley earth-fill structure with a central core anchored into the underlying <br />alluvium. It was thought that seepage from the Pond was Wowing beneath the embankment <br />through the neaz-surface alluvium and through more transmissive units in the underlying Creede <br />Formation. The features that were constructed to intercept and collect the seepage at the Lower <br />Tailings ponds are listed below. <br />Homesmke ALnmg Comporry Shepherd ,11iNer. /nc. <br />ytll "dNUulIJuR~ryi 4 dpnl l{, /99f <br />