Groundwater and surface water quality around a mine constitutes a major part of a mine environmental permit. Understanding mine water quality and its environmental impacts are something that must be investigated not just during the mine operation but also even 100 years or more after closure.

In this study, groundwater and surface water quality was modelled around a mine site with the goal of understanding the effect on water quality around the mine during its current operation, mine production expansion, and closure. The groundwater hydrology of the mine was first modelled using MIKE-SHE while the surface water hydrology was modelled using MIKE-HYDRO. A multi-component reactive transport modelling was performed using PHREEQC incorporating the transport parameters obtained from the results of the groundwater hydrology. The reactive transport modeling subdivided the study area into different zones that have specific geochemical and hydrological characteristics. These zones are the tailings dam, dam crest, moraine and glacial sediments. Input parameters used in these models are: material properties of the geologic units and mine facilities (tailings dam, dam crest, clarification pond); geochemical mineralogy data; surface and groundwater analyses; meteorological data; and hydrogeological parameters. These input parameters are based on the mine database, field sampling and observations as well as publicly available sources. Calibration of the models was carried out using existing water quality data downstream of the modeled areas. Once calibrated, the models were run for other time scenarios.

Modelling results show good agreement with the existing water quality. A potential increase in mine production will also increase constituent elements in the modelled groundwater and surface water. Attenuation of metal transport was notable in the moraine and glacial sediments due to the strong presence of hydrous ferric oxides. The closure and post-closure scenarios of the mine shows lowering concentration of all constituents.

The results from these models provide a basis for a mine environmental permit application. These models also provide guidance on potential water quality risks that must be addressed and water management measures that must be implemented to make sure water quality around the mine remains within the set limits of regulatory agencies. In addition, these models provide a good picture of the hydrodynamics and water quality, their effect to mine operation, natural ecosystems surrounding the mine, communities and other stakeholders.

The Hg-district of Mt. Amiata (Tuscany, central Italy) has been one of the most famous mining areas worldwide for the production of liquid mercury from cinnabar(HgS)-bearing ore deposits and the mining site of Abbadia San Salvatore was by far the largest exploiting and productive center of the whole district. Since 2010, a reclamation project started and operated by the local municipality. To date, the most contaminated represents about 9% of the 65 ha into which the mining structures and metallurgic plant were deployed, i.e. where furnaces (Gould, Nesa and the already demolished Cermak-Spirek), condensers and driers occur. Here, the remediation is expected to be completed next year. Presently, no solutions have been proposed to reduce the concentration of dissolved and particulate Hg in the surface waters and the shallow aquifer system.

Since 2013 a large dataset of geochemical parameters, including Hg, As and Sb, has been compiled and including about 40 geochemical surveys carried out for upstream and downstream waters, as well as those occurring within the mining area. Interestingly, a great seasonal variability in terms of geochemical facies and concentrations of main and trace solutes was observed. Setting aside a few exceptions, the pH values are mostly circumneutral with relatively low total dissolved solids (TDS) that in most cases was <1000 mg/L).

Nevertheless, strikingly high concentrations of Hg were determined in the filtered (up to 2-300 mg/L) and unfiltered (up to 650 mg/L) aliquots whereas those of As and Sb were only occasionally above 10 mg/L. The construction of a channel that crosscuts the whole Hg-contaminated area has limited the interaction between meteoric waters and ore deposits and tailings occurring all over the mining area.

Thus, the new hydrogeological conceptual model and the geochemical data suggested that the Hg-contamination is presently limited to the mining area, since Hg concentrations >1 mg/L were only rarely measured in the surface waters and shallow aquifer downstream the mining area. Additionally, the terrains that host the shallow aquifer have a very low transmittivity and the amount of water to actually be treated is thought to be relatively low. All these hydrogeochemical data were preparatory for testing specific adsorbent materials able to remove mercury according to the pH and TDS values and geochemical facies of the analyzed waters. A pilot site is indeed planned shortly to apply the encouraging laboratory results directly in the field.

Waste rock is a ubiquitous mining waste often produced in large quantities as rock mass surrounding the orebody is extracted from the subsurface. The waste rock is frequently stored at the land surface in piles that may be more than 100 m in height and cover several square kilometers. These piles may be temporary features during active mining operations with the waste rock ultimately backfilled into open pits and underground workings at the cessation of mining; however, more often they become permanent fixtures in the landscape. As the waste rock piles are constructed, fresh rock surfaces are exposed to atmospheric conditions with the potential for the development of poor-quality water. Mine permitting and development require estimation of water quantities emanating from these facilities which, together with geochemical assessment of water-rock interactions within the waste, allow effective short- and long-term planning for water management and treatment. As part of mine planning and operation of waste rock facilities, a large number of scenarios may need to be evaluated to address variants in mine development schedules and permitting requirements. Furthermore, extensive sensitivity analyses of predicted seepage quantities are commonly needed to adequately account for uncertainty in waste rock properties and climate variability.

Within this framework, this study presents efficient methodology for estimating waste rock water balance components (e.g., overland flow, evapotranspiration, infiltration, and basal drainage) using HydroGeoSphere, a physically based, fully integrated, groundwater-surface water numerical code. A suite of numerical simulations was developed to illustrate key concepts and considerations affecting the waste rock water balance during construction and closure for a range in waste rock parameters and climatic conditions. Simulations were conducted using quasi-1-dimensional vertical columns of waste rock material; however, the methodology is easily extendable to two- and three-dimensions. Results of the study indicate the importance of both considering the transient build-out of the waste rock pile during construction and the influence of cover materials at closure on predicted drainage rates reporting to the base of the simulated piles. The analysis framework presented in this study can readily be applied at mine sites in various climatic conditions and waste rock types ranging from “soil-like” materials commonly encountered in coal operations to “rock-like” materials characteristic of hard rock settings.

Mining activities can affect water quality long after the mines have closed. This study focuses on the current status of water in two abandoned gold mines - Crocette and Pestarena - in the Western Alps (Piedmont, Italy). Surface and groundwater samples were collected in three monitoring campaigns in 2024. The results showed arsenic contamination in 75% of the samples. Contamination by aluminium, iron, lead, manganese and nickel was also found in groundwater close to the tailings. These results highlight the long-term impact of abandoned mining activities and the need for continuous monitoring to assess environmental and human health risks.

The nature of groundwater flow and solute transport modelling at and near mine sites has evolved because the objectives (the questions) have changed, simulation software has improved, model resolution has increased, graphical interfaces have become very powerful and stakeholders are asking more challenging questions, especially related to prediction uncertainty. Computing performance has increased by a factor of 10⁶ or more (cf. Moore’s Law and its corollaries), but stakeholder expectations have increased dramatically, so the time required to develop, test and apply a simulation model is not significantly less than it was 40 years ago. High-level modellers still need programming skills to extend available simulation software.