Performance assessment of a single-layer moisture store-and-release cover system at a mine waste rock pile in a seasonally humid region (Nova Scotia, Canada)
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Cover systems are commonly applied to mine waste rock piles (WRPs) to control acid mine drainage (AMD). Single-layer covers utilize the moisture “store-and-release” concept to first store and then release moisture back to the atmosphere via evapotranspiration. Although more commonly used in semi-arid and arid climates, store-and-release covers remain an attractive option in humid climates due to the low cost and relative simplicity of installation. However, knowledge of their performance in these climates is limited. The objective of this study was to assess the performance of moisture store-and-release covers at full-scale WRPs located in humid climates. This cover type was installed at a WRP in Nova Scotia, Canada, alongside state-of-the-art monitoring instrumentation. Field monitoring was conducted over 5 years to assess key components such as meteorological conditions, cover material water dynamics, net percolation, surface runoff, pore-gas, environmental receptor water quality, landform stability and vegetation. Water balances indicate small reductions in water influx to the waste rock (i.e., 34 to 28% of precipitation) with the diminished AMD release also apparent by small improvements in groundwater quality (increase in pH, decrease in sulfate/metals). Surface water quality analysis and field observations of vegetative/aquatic life demonstrate significant improvements in the surface water receptor. The WRP landform is stable and the vegetative cover is thriving. This study has shown that while a simple store-and-release cover may not be a highly effective barrier to water infiltration in humid climates, it can be used to (i) eliminate contaminated surface water runoff, (ii) minimize AMD impacts to surface water receptor(s), (iii) maintain a stable landform, and (iv) provide a sustainable vegetative canopy.
KeywordsAcid mine drainage Contaminant remediation Hydrogeochemistry Environmental monitoring Water balance Landform stability
This work was conducted under the CAPs Monitoring Project and funded by Enterprise Cape Breton Corporation (ECBC) which was later dissolved into Public Works and Government Services Canada (PWGSC). The authors wish to thank the anonymous reviewers for their helpful comments towards the improvement of this paper. Special thanks are given to Joseph MacPhee and Joseph Shea (PWGSC) and Devin MacAskill (Cape Breton Regional Municipality, CBRM) for their support during this study. The authors would also like to acknowledge Greg Meiers (O’Kane Consultants) for sharing his expertise, along with David Mayich, Fred Baechler (exp Consultants), and Jamie Tunnicliff (Stantec Consulting Ltd.).
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