The Iberian Pyrite Belt (IPB) is located in the southwest of the Iberian Peninsula, hosting the largest concentration of polymetallic massive sulfide deposits in the world. Due to heavy mining and processing of ores since the times of Romans, large amounts of mining wastes are dispersed along this geographical area, which are called as “legacy sites”. Many of these wastes contain huge levels of toxic metals and metalloids (e.g. As, Cd, Cu.) and are also potentially NORM (Naturally Occurring Radioactive Materials) wastes, which can constitute an important environmental threat and a substantial potential public health and safety problem.

Therefore, a novel radioactive and physicochemical characterization of the most relevant mining wastes located at different points of the IPB was performed. To this end, wastes have been sampled in different mines, and a multi-elemental, mineralogical and natural radionuclide analysis has been done on each of the samples collected. Forced leaching experiments have also been done to assess the release capacity of contaminants when they come into contact with water. Finally, a diagnosis of potential lines of valorization was made to provide a solution and viability for the environmental effects caused by mining wastes.

The radionuclides activity concentrations of both ²³⁸U and ²³²Th decay series, and ⁴⁰K, were in the same order of magnitude as those expected for undisturbed soils in this geographical area, about 30, 50 and 700 Bq/kg, respectively. In addition, some disequilibria radioactive between long-lived radionuclides from the same series were found, mainly produced by the physicochemical process where they are produced. On the other hand, highly toxic elements such as As, Cu, Pb or Zn, in few wastes, exceed the concentrations in μg/g for uncontaminated soils by 3-4 orders of magnitude. Finally, wastes have an equivalent radius value (Ra_eq), external radiological hazard index (H_ex) and activity concentration index for emitted gamma radiation (Ic) lower than the threshold values stablished.

The potential valorization lines for the use of these mining wastes have been also analysed. From a radiological point of view, wastes would comply with the marketing regulations in the USA, and EU regulation to be reused in construction materials.

Hydrogeological studies in mining are traditionally aimed at tackling problems of safer development of mineral deposits. In recent years, a large number of deposits have been decommissioned both around the world and in Russia, which has made it imperative to solve the problems of post-closure management of sites disturbed by long-term mining operations. The principal types of influence are almost identical in different countries and do not depend on the type of mineral: these are changes in the condition of the underground and surface waters, instability of the earth's surface, and leakages of toxic gases or hazardous substances into the environment. Management of depleted deposits, especially old and abandoned mines, has necessitated the development of special laws and investment of substantial funds in mining area remediation.

In the early 21st century, coal mining in the Chelyabinsk coal basin (Southern Urals, Russia) was terminated. Mining operations in this area of 1,300 km² had continued for over a century, accompanied by dewatering (700 L/s). During that time, a number of towns and settlements with a population of about 300,000 people appeared near the mines. The cessation of the dewatering process has been accompanied by a number of phenomena: the groundwater balance is changing; the sources of surface water recharge are being redistributed; the settlement areas are exposed to flooding; landslides occur on the pit slopes, and sinkholes are forming in subsidence areas.

The first-ever regional groundwater flow model has been developed, which has enabled us to assess the consequences of mine and open-pit flooding; maximum groundwater levels and a time frame for reaching them have been determined. The forecasts consider the influence of climate changes both in the longer term and annually with reference to the probability of precipitation redistribution. The filling of the depression cone is almost complete, and the groundwater levels have stabilized. The open pit workings will continue flooding over the next 70 to 200 years.

Studies have established that at the post-closure stage, the duration of which is estimated at tens and even hundreds of years, new hydrogeoecological conditions are emerging: the lakes that existed due to mine drainage are drying up, and a relevant deterioration of water quality in them is taking place. The complexity of the processes at the post-closure stage is determined by a combination of structural geological features and geomorphological conditions, hydrometeorological factors and mining methods.

Over a hundred lignite-mining pit lakes exist in East Germany, most of them flooded for more than a decade. A specially developed monitoring program tracks their hydrological and chemical conditions and, encouragingly, many lakes show progress towards stable conditions. In recognition, 16 pit lakes were included in a preliminary monitoring under the European Water Framework Directive, which provides a standardized framework for assessing lake water quality across Europe. The coexistence of these two monitoring systems has prompted consideration of potential synergies. However, a comparison reveals differences in frequency, parameters, and quality requirements. Ultimately, defining ‘stable lake water quality’ remains the key relinquishment criterion to conclude the mining-hydrological monitoring.

Designing robust stormwater management infrastructure at mining sites requires accurate estimates of runoff rates in response to design storm events. Standard practice for event runoff estimation is to develop a surface water hydrology model that is calibrated to reproduce the runoff response for historical storm events at gaged locations in the catchment. The calibration lends confidence to the model’s ability to predict conditions during a future event. At mine sites where reclamation is in progress, model calibration is complicated as the reclamation work can change the landforms and surface cover in ways that modify the surface water response characteristics.

This study evaluated the changes in catchment response to progressive reclamation of the Upper Wanagon overburden stockpiles at the Grasberg Mine in Indonesia. The stockpiles occupy approximately 350 hectares. Progressive reclamation of the stockpiles commenced when overburden placement ended in 2018. As of 2024, reclamation work has been completed for approximately 250 hectares. Reclamation includes regrading to direct surface runoff into engineered channels that are armored with riprap. To mitigate erosion, the overland surfaces are covered with a rock armor and vegetated.

These closure activities alter surface water runoff. For example, regrading of the stockpiles has altered flow paths and reduced surface depressions. Also, installation of rock cover and vegetation has roughened the overburden pile surface. These activities alter the runoff volumes and the rate at which runoff flows are conveyed. Accounting for these alterations in predictive runoff models is a challenge for the Upper Wanagon reclamation design.

Rainfall gauges and a surface water flume at the catchment outlet provide rainfall and runoff measurements for the Upper Wanagon area pre- and post-reclamation. Review of this data and subsequent model calibration provides insight on how reclamation affects the runoff responses. This work explores these impacts, and the findings are used to inform reclamation design and post reclamation stormwater management.

Historic salt mining at Carrickfergus, Northern Ireland has left a legacy of hazards including surface subsidence and land contamination through brine water discharges. An area of three abandoned mines, hydrologically connected to facilitate solution mining, underlies a public road network, public water supply intake and gas transmission pipeline. Post closure, the site is undergoing active subsidence resulting in crown-hole development and a series of large brine discharges at surface contaminating the surrounding lands and watercourses.

Multi-geophysical techniques using seismic and electrical resistivity surveys combined with electrical self-potential surveys were conducted to characterize the geological and hydrological processes driving the mining hazards. Water and salinity levels within the connected mines are recorded through a network of monitoring boreholes. Surface motion data is measured using terrestrial levelling and satellite Interferomatic synthetic-aperture radar (InSAR). Using these combined methods, we have been able to characterize the linkages between mine water levels and surface instability and, in turn, surface subsidence and highly saline brine migration to surface.

Results from the geophysical surveys identified compositional changes and deformation altering the geochemistry of the groundwater. Water ingress to the underlying strata from crown holes has led to gravitational slumps as a result of dissolution of the halite bearing strata. This has resulted in deformation and stepped thrusts coincident with brine migration to surface. The occurrence of brine migration to surface is more prevalent following surface subsidence as a hydraulic head in the deep mine induced by freshwater injection to the crown hole at surface promotes the movement of saline waters through pathways created by weaknesses within the strata, boreholes and shafts leading to extensive land contamination events. Ground motion data acquisitions combined with water level data show a correlation with decreasing water levels within the mine as a result of surface brine emissions and increased subsidence at surface, which, in turn, lead to further water ingress pathways in a repeated cycle.

Presently, a high-density network of satellite InSAR reflectors, GNSS stations and precise levelling points are developing across the site to gain an increased understanding of mine water level controls on surface instability. Combined with mine water data, information will enable early escalated actions to be taken to mitigate mining hazards.