Monitoring for pit lake planning, filling and use: Why? When? What?

Authors: Schultze, M; Vandenberg, J; Castendyk, D; Schleußner, H-P; McCullough, CD Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2415_75

Cite As:
Schultze, M, Vandenberg, J, Castendyk, D, Schleußner, H-P & McCullough, CD 2024, 'Monitoring for pit lake planning, filling and use: Why? When? What? ', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2024: Proceedings of the 17th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1049-1062, https://doi.org/10.36487/ACG_repo/2415_75



Abstract:
Pit lakes are important features of many open pit mines that can represent risks for humans and the environment, but may also offer beneficial end uses. Risks related to pit wall stability, water balance and water quality can be expensive to mitigate and may represent long-term liabilities for mining companies and stakeholders. Two key factors in closing pit lakes successfully are early planning and careful management, both of which require vigilant and early monitoring and data collection. Depending on the phase of the mine and particulars of the pit lake and socio-environmental context, the purpose and scope of monitoring will change. The reasons for monitoring the pit lake as it evolves through the life of mine changes, as it progresses from planning to operations to closure. Monitoring should start as early as possible, although different mine phases require different focus and intensity. For instance: during mine planning and operations: defining closure criteria; generating model forecasts of future water balance/quality trajectories; identifying and characterising environmental risks and potential beneficial end uses during pit lake filling: continually appraising modelled trajectories and adaptive management strategies once full: demonstrating success criteria are achieved consistent with closure criteria to validate pit lake relinquishment post-closure: demonstrating continued physical and chemical stability consistent with the requirements of the intended end use. What should be monitored depends on the specific pit lake, its external factors and internal processes. External factors comprise: climatic, meteorological and resulting hydrological conditions; geological, geotechnical and geochemical circumstances of the orebody; host and country rock, including design and placement of waste landforms. Internal processes comprise: lake mixing; biogeochemical reactions; lake/groundwater-sediment interactions; cycling of nutrients and oxygen; ecosystem development and intended post-mining land use. Herein we discuss why, when, and what parameters to monitor for pit lakes in order to inform planning, closure, and post-closure end use implementation.

Keywords: mine closure, closure criteria, pit wall safety, water balance, water quality, pit lake, monitoring

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