Hydrologic characterization of two full-scale waste rock piles

• Main Author: Fines, Pamela Elizabeth
• Language: English
• Published: 2010
• Online Access: http://hdl.handle.net/2429/17836

Waste stockpiles pose an environmental risk for leaching of metals and low pH water long after a mine has stopped operations. To determine the potential for acid generation in waste materials a clear understanding of flow through the waste rock piles is required. Based on field and laboratory investigations, this research focuses on developing an understanding of flow mechanisms through waste stockpiles. Two mine sites were selected for the fieldwork. The fieldwork was conducted while the waste rock material was being replaced in the open pit for closure. The relocation of the waste rock dump allowed for in-situ observation and testing of the materials stockpiled. The field investigations included excavation of test pits in each bench of the waste rock pile during relocation, logging of structure and materials present, and in-situ testing for density and matric suction. The laboratory investigations comprised the determination of grain size distribution, water content, paste pH, Soil Water Characteristic Curve, and saturated hydraulic conductivity. The field and laboratory data was used to develop conceptual models of flow for each waste rock pile. These models were based on the observed structure and material properties determined in the laboratory. The typical observed structure included inclined dense layers at the angle of repose, weathered waste rock, and traffic surfaces. The conceptual flow model at Site 1 was evaluated using a finite element seepage analysis program. The modeling clearly shows that preferential flow develops within the waste rock pile. Leaching of soluble minerals out of the dump will be governed by flow paths of infiltrating water and these paths can be estimated based on field observations and numerical modeling. The structure at Site 1 showed evidence of interbedded layers and this structure controls the flow paths developed within the dump. Predictions of which materials will be the dominant flow paths, and subsequently which minerals are most likely be to be mobilized can be estimated for any waste rock dump if there is knowledge of the hydraulic and geochemical properties of the waste rock and internal structure within the dump. === Applied Science, Faculty of === Mining Engineering, Keevil Institute of === Graduate