An Anoxic Limestone Drain (ALD) and Open Limestone Channel (OLC) are primary components of the Project for the Restoration of Rio Juckucha, in Potosí, Bolivia; the goal of which is to improve water quality for irrigation use in the high Andes. The OLC is treating low-pH (2.9) acid mine drainage from a man-made alpine lake receiving discharges from portals, tailings, and waste-rock from active and abandoned mining operations. The ALD is treating milder acid mine drainage (pH 5.4) from an abandoned mine portal. Both systems treat waters that run to Laguna Santa Catalina, which forms the headwaters of Rio Juckucha, a key irrigation water resource. The alkalinity generation and metals removal performance of the recently-constructed ALD and partially-constructed OLC was investigated to determine early-stage treatment characteristics. The results indicated that the OLC at 20% completion was having relatively little impact. The recently-constructed ALD is showing water quality improvements (higher pH and alkalinity). However, there is a concern with increased Zn and Mn concentrations in the ALD effluent. Studies will continue upon construction completion to determine long term performance.

Abstract:The historic mining center of Cerro Rico de Potosí, Bolivia is marked with many tailing piles, with the Pailaviri tailings deposit being of great concern. These polymetallic sulfide tailings release some of the highest concentrations of ecotoxic metals observed in natural waters. In order to obtain a deeper understanding of the deposit, water samples were taken in transects throughout the deposit. Total metal concentrations in the waters were extremes: Al (25-2.9 g/L), As (1700-330 mg/L), Cu (850-140 mg/L), Fe (100-24 g/L), Mn (110-70 mg/L), Pb (36-21 mg/L), and Zn (3.1-1.9 g/L). Dissolved concentrations were essentially equivalent indicating these metals were in aqueous phase. Sulfate ranged from 136 to 400 g/L. Due to the extremely acidic nature of the water, the pH probes quickly degraded and became inoperable, rendering accurate pH measurements impossible. These results provided evidence of highly toxic conditions and likely downstream impacts due to close proximity of Rio Huayna Mayu. The extremely elevated concentrations of metals indicate that the Pailaviri deposit may be reprocessed at a profit and safely disposed of, an option which should be investigated.