Evaluation of mine dewatering and related impacts at a deep underground iron mine in northern Sweden

摘要

The Kiruna underground iron mine in northern Sweden is expanding to deeper mine levels. To continue with mine expansion and continued operation, the mine owner, Luossavaara-Kiirunavaara Aktiebolag (LKAB), is required to obtain permits through the Environmental Court in Sweden. As part of the permit application, potential impacts to surface water and groundwater resources near the mine are being evaluated. To assess potential impacts of mine expansion on water resources, a linked surface water-groundwater model is being developed. The surface water model of watersheds surrounding the mine, including the Luossajoki River-Lake Yli Lombolo-Lake Ala Lombolo flow system, focuses on understanding the potential impacts of the mine on the surface water flow system. The regional groundwater model focuses on forecasting mine dewatering rates and predicting potential impacts on groundwater levels near the mine, especially near Lake Ala Lombolo and in the town of Kiruna where private wells exist. The groundwater and surface water models are linked through watershed recharge and seepage between surface water and groundwater. Modelling of the surface water-groundwater system is complicated by the predicted expansion of the deformation zone with continued deepening of the mine. The Kiirunavaara ore body dips about 60 degrees to the east (E) towards the town of Kiruna. Continued mining of the ore body has resulted in a gradually increasing zone of ground deformation. The expanding deformation zone not only results in impacts to the town and infrastructure, but also creates continually-evolving surface water and groundwater hydrology. Aquifer material properties are varied linearly through time in the groundwater model to accommodate the expanding deformation zone. The expanding surface expression of the deformation zone enhances recharge and increases mine inflow with time. Uncertainty in mine inflow is highest for prediction of recharge and the deformation zone extent. Using estimated upper and lower bounds for these model parameters, a feasible range of mine inflows is calculated for the 20-year (yr) prediction period.