Laserfiche WebLink
that the indicated base of the dike over 5 feet below the <br />• static water level in MW 4. <br />The distributions of anomalous iron, lead, copper, zinc and <br />manganese concentrations suggest long term leaching from old <br />tailings; both the old Pride tailings pond and tailings <br />redeposited in the Animas River flood plain west of the new <br />tailings pond. The distribution of anomalous zinc and <br />sulfate concentrations is mare wide spread and could <br />represent the downward percolation of impounded decant <br />water. However the source of the anomalous values west of <br />the new pond is believed to primarily be the leakage of <br />tailings liquors through the permeable pond dil<e, while the <br />new pond's decant system could also have been a contributor. <br />The decant pipe inlet is located in the northwest portion of <br />the new pond, approximately 50 feet south of sample site no. <br />19, while the discharge is understood to have been <br />immediately west of the dike. <br />As the north and east sides of the new pond are in hydraulic <br />communication with the surrounding alluvium, the ground <br />water appears to be transporting the contaminants <br />southwesterly to an area of surface discharge with in the <br />confines of the breached seepage retention pond south of the <br />old pond. A reconnaissance of this area including testing <br />the surface waters for pH and the presence of iron by <br />• collecting 25Q ml samples and adding NaOH pellets. Copius <br />quantities of green ferrous iron precipitates were noted. <br />The pH values ranged far 5 to 6.5. The strongest reactions <br />were at the discharge of the two previously described decant <br />chimnies. However; seepage from a horizon appro>imately 1 <br />foot above the base of the south di4:e of the old pond also <br />displayed a strongly positive iron reaction to NaOH. Strong <br />ferrous reactions were also noted with samples from wells <br />M4A and M4B, (sites 7 and 5). The water contained within the <br />old tailings as represented by water collected from a <br />shallow, 5 feet deep monitor well (site 6) is highly charged <br />with zinc iron, manganese, cadmium and sulfate, indicating <br />again that the source of these parameters is the old <br />tailings. The implication is that the contamination of <br />ground water under the old tailings pond will continue for <br />many years and this water will, in turn, move southward to <br />the east branch of the Animas River unless prevented from so <br />doing by the construction of an impoundment or treatment <br />facility. The zinc and pH parameters of these waters exceed <br />current EPA effluent limitations far existing source <br />discharges from flotation mills processing base and precious <br />metals ores. As dicussed in the Site Hydrology section, the <br />discharge from under the old pond consists of a number of <br />separate ditches and near suface sheet flow through <br />• -14- <br />