Integrating the effects of roots on the geoenvironmental behaviour of cover systems used to reclaim mine waste storage facilities

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Engineered cover systems are used across Canada to mitigate environmental issues, such as acid mine drainage, associated to the storage of mine wastes. Acid mine drainage occurs when reactive mine wastes are in contact with atmospheric oxygen and water. Cover systems are designed to stop water and oxygen migration down to the reactive wastes they cover, thanks to targeted properties of their materials at construction. With time, cover systems are colonized by plants coming from adjacent ecosystems. Plants change the water content and movement in cover systems. More specifically, plant roots pump water and modify the physical, chemical and biological properties of cover materials. Thus, plants may affect the performance of cover systems to control the undesirable contact between water and/or oxygen with the reactive mine waste they cover. To predict the performance and design cover systems, engineers use numerical models of water budget, which can include vegetation's effects. But the prediction of the vegetation effects is often inaccurate. This mainly comes from the lack of values of vegetation parameters specific to the context of mine cover systems. In particular, root development is expected to be specific in cover systems, especially those constructed with several layers of differing materials (i.e. multilayered), but root studies in this context are scarce. Moreover, root dynamic growth and effect on the water movement in the cover system materials (i.e. effect on hydrogeotechnical properties) is not taken into account for the moment. The long-term objective of this research program is to improve and develop knowledge on the interactions between plants and engineered cover systems, with a focus on roots, to better predict the evolution of their performance with respect to ecosystem processes. This interdisciplinary research program will provide integrated root, hydrogeotechnical, and water budget data in the specific context of multilayered cover systems, with a focus on covers with capillary barrier effect used under humid climates. It will use field-scale and controlled laboratory monitoring, as well as numerical modeling. This work will decrease the uncertainty of vegetation parameter values required to design sustainable cover systems in the long-term. It will also document the evolution range of the hydrogeotechnical properties of cover system materials colonized by vegetation, especially mature trees. The research outcomes will constitute a knowledge basis for larger application to other waste containment technologies. A postdoc, 3 HQP and 3 UG interns will acquire interdisciplinary skills and will be able to design reclamation technologies responding to industrial, government, and communities' needs.