Environmental issues play an increasingly important role in planning large-scale mining activities. Potential impacts are often related to groundwater systems, which may be inadequately understood and assessed. This is especially true in Lapland where subsurface and surface water reserves and their hydraulic connections have rarely been studied. The Hannukainen iron–copper–gold mining development site is surrounded by three rivers,
identified as critical spawning grounds for sea trout, an endangered species. Therefore it is essential to assess the potential environmental impacts of the planned mining to associated groundwater and surface water bodies. We described the aquifers and aquitards, measured or calculated hydraulic conductivity of hydrostratigraphic units and observed hydraulic heads and groundwater flow directions as well as characterized chemical and isotopic signatures of waters. The specific objective was to evaluate the groundwater–
river water interactions. Based on the sedimentological and hydrogeological studies as well as ground penetrating radar survey, the Hannukainen site hosts a complicated aquifer system with notable connections to natural
river systems. The Quaternary sediments are exceptionally thick, representing a dynamic development during the Mid Weichselian. The glacial strata can be divided into three hydrostratigraphical units: the lower, middle and upper aquifer, separated by aquitards with low permeability. Aquifers are related to fluvial and deltaic sands and gravels. Aquitards relate to tills and/or fines hosting intricate perched water bodies. According to water and riverbed sediment temperature observations and stable isotopic composition of waters, the hydraulic head measurements and low altitude aerial infrared (AIR) survey, rivers Kuerjoki and Valkeajoki are dominantly fed by groundwater. The hydrogeological analysis presented
here was found to be useful in siting mining facilities such as tailings. At Hannukainen, the mining company decided to operate within a more restricted area and to move the tailings management facility away from the most sensitive area, to avoid undesirable environmental impacts.