1985-12-22_HYDROLOGY - M1984049 - Laserfiche WebLink

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for that year was 1200 cfs, occurring on June 23rd. The high • peak flows indicate that This is evidenced by the partial destruction of the dikes constructed adjacent to the river by previous operators contemplating the e>;pansion studied in 1980. Of particular concern are the di4:e separating the Phase III and Phase IV er.pansions and the west dikes of the Phase III & IV er.pansion ponds. The latter has been breached and waters from the Animas River flow into the pond created by er.cavating material to build this dike. This area has been used for the disposal of derilect equipment and supplies and appears to contain seepage from the old pond. The dike should be repaired and the scrap be removed and disposed of properly as in its present state the area is a potential source of pollution. Mineralized water from this same pond is seeping through and below the south dike into the open marshy area south of the old ponds where it combines with highly contaminated flows emanating from the dike and from below the old tailings pond. Precipitation runoff from the old pond flaws down through the decant chimney of the old pond and discharges out the south dike in to this same marshy area. As the decant chimney is terminated 15 to 18 inches below the grade of the tailings pond, a rivelet has been cut 15 to 18 inches into the old tailings, which are being eroded into the Animas River. Both • these decant chimnies should be sealed and replaced with a proper spillway structure for emergency discharge. The invert should be elevated above the pond surface sufficient to provide adequate dilution of the impounded water. A sediment-seepage impoundment once e:;isted south of the old and Phase IV er.pansian ponds; however floods have breached most of the dike forming this impoundment. Contaminated seepage flows now reach the Animas River. This di4:e should 6e repaired. The previously described Phase III & IV Er,pansion dikes should also be repaired to prevent flood waters from inundating this seepage control pond and destroying its di4;e. Contaminated water from under and within the old tailings pond flows southward through this area in several ditches and as near surface sheet flow in the permeable alluvium. These flows discharge into an east branch of the Animas River up stream from sample site no. 23 (refer to Figure Nos. 3-13 ). The subsurface regime consists of a shallow unconfined aquifer in the alluvium of the Animas River valley and ground water flaws seeping to surface at the east side of the pond. This latter flow emanates from surface and subsurface flows in a gulch cut into the mountains forming • -10-