Relocation of net-acid-generating waste to improve post-mining water chemistry

Acidic drainage and metal leaching are long-term environmental liabilities that can persist for many decades to millennia. One technique to improve th e water chemistry and ecology of post-mining landscapes is to relocate and submerge net-acid-generating mine materials in a lake or water-retaining im poundment. One example of a carefully executed relocation of waste rock too k place at the Eskay Creek Mine in Canada. Pre-relocation studies included an empirical relationship that related (1) the amount of acidity retained b y the waste rock during past oxidation to (2) the amount of lime needed in each truckload for neutralization of the acidity and for suppression of met al release. During relocation, thousands of rinse pH measurements indicated net acidity varied significantly over short distances within the waste roc k and that acidic rock could not be reliably segregated from near-neutral r ock. After relocation, water from the watershed continued to be acidic for a few years, then returned to near-neutral pH and near-background concentra tions of metals. The chemistry of the lake where the waste rock was submerg ed remains near background conditions. Therefore, with careful planning and implementation, the relocation and submergence of net-acid-generating mate rials can greatly improve post-mining water chemistry. (C) 2001 Elsevier Sc ience Ltd. Al rights reserved.