Long-term Field Performance of Geomembrane-Lined Cover Systems at Mine Waste Rock Piles

Mine waste rock piles (WRPs) are anthropogenically created landforms at active and former mining sites that can generate and release highly toxic acid mine drainage (AMD) to the environment. A common solution to control AMD generation is the use of cover systems at the WRPs to isolate the reactive waste from water and oxygen in the atmosphere. Geomembranes exhibit the characteristics needed to be highly effective barriers to atmospheric influx; however, knowledge on their performance at in-service WRPs is limited. The objective of this thesis is to comprehensively assess the field performance of geomembrane-lined cover systems for limiting meteoric water to the waste rock. Four coal mine WRPs located in the Sydney Coalfield in Nova Scotia, Canada, were reclaimed with different cover systems and then extensively monitored for seven years. Defect leakage and water balances methods were employed to determine the daily water flux through the cover systems at each WRP over seven years. Results demonstrated that the inclusion of geomembrane liners in cover systems reduced the water influx from 28% of precipitation to as low as 0.05%. Furthermore, the composition of the drainage layer overlying the geomembrane influences the water influx, with native soil, granular material and geocomposite nets providing influx rates of 3%, 0.5% and 0.05%, respectively. This thesis highlights the role of geomembrane liners and drainage layers in engineered cover systems for significantly limiting the influx of meteoric water to mine waste rock