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ar r ' <br />• <br />outside the pond. Two locations were near the lower limit of <br />• detection; however three ground water locations under the <br />new pond and one north oh the pond contained significant <br />concentrations of cyanide. The three anomalous location <br />under the new pond are near the site of a recent gold heap <br />leach es:periment where sodium cyanide was employed. The <br />cyanide detected in the impounded water and under the pond, <br />as well as in the ground water just north of the pond, is <br />believed to be derived from that es:periment. It is possible <br />that impounded surface water containing cyanide seeped <br />through the dike and entered the ground water near this <br />point (monitor well MW 4). The ability of the pond to drain <br />through its dikes is indicated by the differences between <br />the 1980 and 1985 water levels in the pond dikes. <br />Low concentrations of mercury were found at essentially the <br />same locations as the cyanide. Grab samples of tailings <br />solids indicated the old pond tailings average 1.2400 ppm <br />mercury while the new pond solids average 0.2400 ppm. These <br />concentrations are several hundred fold greater than the <br />those of the filtered water samples, indicating the tailings <br />are the source of the mercury. The association with the <br />cyanide may be due to the dissolving action of the cyanide. <br />The possibility of the heap leach er:periment as a source for <br />the cyanide is supported by the fact that, except for the <br />presence of cyanide, the quality of the water presently <br />• impounded on the pond is very close to that of the inflow <br />water as indicated 6y the sample collected at the <br />interceptor drain, The relatively low concentration of other <br />parameters at sites 1, 2 and 3 may represent a flushing <br />effect of the ground water flow from the east while cyanide <br />is being continually transported downward through the <br />tailings from the er.periment site by precipitation. <br />No significant concentrations of arsenic, silver nor <br />chromium were detected; however high concentrations of <br />cadmium, iron, manganese, zinc and sulfate were detected <br />under the new and old ponds and discharging into the east <br />branch of the Animas River in the vicinity of site 23. High <br />concentrations of these same parameters were also detected <br />in the ground water underneath the old pond at site no. 9 <br />(monitor well M 15). High concentrations of these same <br />parameters were found in monitor well M 20 (site no. 13) and <br />high values for sulfate and iron were noted in monitor well <br />MW 4 (site no. 17). The high concentrations at M 20, located <br />300 feet west of the pond, is believed to be the old <br />tailings in the vicinity of this well. The source at MW 4 is <br />believed to be tailings pond leakage through the dike. The <br />tailings pond is deeply incised in the vicinty of MW 4, such <br />• -73- <br />