The Monday Creek Restoration Project is a program of Rural Action, a non-profit organization committed to improving watershed health in Appalachian Ohio. Monday Creek is a stream impaired by acid mine drainage (AMD) and other pollutants. Previous studies have identified Snow Fork as the tributary with the greatest AMD contribution to Monday Creek, therefore the Snow Fork Dosers project was proposed for design and construction with project oversite provided by Ohio Department of Natural Resources, Division of Mineral Resources Management, with funding from Ascent Resources. The Snow Fork project design demonstrates the potential for stream restoration using active treatment with lime dosing, and the effectiveness of collaboration and perseverance in moving stream restoration projects toward completion.

The project included evaluation of five potential doser sties pre-selected by ODNR with two sites, named “Brush Fork” and “State Route 78”, selected as preferred dosing locations based on comparison of factors including water quality, flooding potential, environmental sensitivity, availability of utilities, site topography, site access, and property ownership. Potential treatment strategies using Quicklime, dry hydrated lime, or hydrated lime slurry were also evaluated. After these determinations, available water quality and historic daily flow monitoring data was used to develop a mathematical relationship between flow and acid concentrations from which lime dosage requirements for treatment were estimated.

The design investigations resulted in the decision to design dosers utilizing dry hydrated lime. Two doser designs were required per the original scope of work, however it was concluded a single doser constructed at the Brush Fork site might achieve the project’s treatment objectives. Therefore it was recommended to bid, construct, and operate a single doser at the Brush Fork site. The performance of the Brush Fork doser would then determine the need for construction of the second doser at the “State Route 78” site.

The cooperation and persistence of the groups involved in moving this project to the bidding phase should serve as motivation to other watershed groups and stream restoration efforts. Although other options are available for AMD treatment, the application of active treatment using lime dispensed directly from “dosers” into impacted waters has been successful elsewhere in Appalachia, and as shown in this design, can be successful at Snow Fork and Monday Creek in Ohio.

Acid mine drainage (AMD) systems are typically characterized by low pH, high concentrations of iron and sulfate, and a wide variety of potential toxic elements. The hydrochemical properties of AMD depend on several factors (e.g., geological context, climate condition, mine waste reactivity, and others), which determine their complexity. In addition to the abovementioned parameters, electrical conductivity (EC) and total dissolved solids (TDS) should be analyzed to understand biogeochemical processes and contamination degree. Although TDS is a crucial parameter for characterizing acid mine waters, their gravimetric standard analysis is time-consuming and expensive. Therefore, TDS is commonly estimated through other parameters, namely EC and acidity.

This study presents an unexplored statistical approach using linear and multiple regression to estimate TDS concentration in AMD. One hundred twenty-one samples were collected from three distinct abandoned mining areas in the Iberian Peninsula: Valdarcas, São Domingos, and Campanario. The parameters analyzed in these samples included pH, EC, TDS, acidity, and sulfate concentration. The study used statistical techniques such as discriminant analysis and simple (SLR) and multiple linear regression (MLR) to identify the best predictor variables of TDS. Summary statistics were calculated to describe each independent variable, including mean, median, standard deviation, minimum, and maximum. The IBM SPSS (v. 28) software was used for statistical analysis.

The chemical analysis in the AMD samples revealed high variability due to the different hydrochemical conditions in the three mining areas. The pH values were found to be in the acidic range (between 0.44 and 4.82), and the concentration of acidity varied from 96 to 429 250 mgL^-1 CaCO₃. The concentrations of sulfate and TDS were between 153 to 410 601 mgL^-1 and 296 to 640 086 mgL^-1, respectively. The São Domingos water samples have significantly lower pH values (p 0.05) when compared to the other mines. Regarding the other parameters under study (TDS, EC, sulfate, and acidity), Valdarcas mine showed statistically significant differences (p 0.05). The results obtained are in good agreement with earlier findings proposing that, for acid mine waters, acidity is a relevant predictive parameter of TDS.

Furthermore, the MLR models suggest that acidity combined with sulfate and EC provide better TDS estimation. However, due to the heterogeneity of the three areas and the complexity of AMD waters, further investigation is required to increase current knowledge of the interactions between the different physicochemical parameters that influence TDS estimation.

Cobalt (Co) is a critical metal essential to the clean energy transition due to its use in lithium-ion batteries. The majority of the global Co supply is extracted using artisanal mining methods that can be destructive to human health and the environment. Alternative Co sources are being explored, including coal mine drainage (CMD) solids, a continuous waste stream from passive treatment systems in Appalachia, USA. CMD solids consist of iron, aluminum, and manganese (Mn)-rich oxy/hydroxides that can contain high levels of some critical minerals. Mn-rich phases in particular have been shown to contain high Co concentrations, up to 6,000 mg/kg, and bear comparison to low-grade Co ores (e.g., 2,000-10,000 mg/kg) (Hedin et al., 2020, doi.org/10.1016/j.coal.2020.103610). CMD is sulfate-rich, and during treatment, CMD solids are accumulated in limestone beds as precipitates over a wide pH range, but Co sorption mechanisms have not been studied under these conditions.

Experimental exploration of abiotic Co sorption mechanisms on different birnessite (d -MnO₂) structure types (hexagonal, H-birnessite and triclinic, Na-birnessite) that are commonly found in Mn-rich CMD solids offers insights into Co retention mechanisms in CMD treatment systems. This study investigates Co adsorption on synthesized birnessites over a wide pH range and in sulfate-rich solution to simulate CMD treatment conditions. Langmuir and Freundlich adsorption isotherms of Co at pH values of 3.5, 4.5, and 6.5 at 25°C onto Na-and H-birnessite were generated. Chelation ion chromatography, developed by Miller et al., 2022, doi.org/10.1016/j.chroma.2022.46292, was the detection method for Co concentrations in supernatants. Mineralogy and morphology of pre- and post-adsorption experiment solids characterization by X-ray diffraction and scanning electron microscopy will be presented.

Cobalt adsorption peaked at pH 4.5 in both structures, although the maximum adsorption capacities of the triclinic birnessite (131 mg Co /g sorbent) was twice as high as hexagonal structure (71 mg Co /g sorbent). Sulfate, a major anion in CMD, decreased the fraction of Co adsorbed on both structures at pH 3.5 and 4.5, but had a modest effect at pH 6.5. These experiments suggest that cobalt sulfate complexes and pH of CMD, as well as the Mn-oxide mineral structures present in treatment beds, will influence cobalt adsorption in CMD solids.

These experimental results can serve as calibration points for equilibrium and kinetic modeling approaches such as PHREEQ-N-AMDTreat+REYs (Cravotta, 2021, doi.org/10.1016/j.apgeochem.2020.104845) that are critical for developing effective and implementable remediation processes and to better inform future Co recovery efforts from CMD solids.

Active and passive treatment methods have been carried out nationwide in the Republic of Korea, contaminating the nearby water system with mine water containing components such as suspended solids (SS) and potentially toxic elements. In particular, active treatment methods, such as slaked lime neutralization treatment and electrochemical treatment, are under operation. Meanwhile, the prediction of settling efficiencies is needed for the appropriate design of treatment facilities.

The settling characteristics of SS in the precipitation tank throughout the treatment process at the mine water treatment facilities in Yeongdong (YD), Hambaek (HB), and Hamtae (HT) abandoned coal mines were identified in order to assess the settling efficiency.

A laboratory-scale column device simulating the settling tank was designed and manufactured to continuously measure the change in turbidity over time to assess the settling characteristics. Water samples from the neutralization/mixing tank, just before entering the settling tank of each treatment facility, were filled in a vertical column with a total length of 2 m using a pump, and the water samples were collected from the sampling ports of various depths every certain period of time to measure SS. Also, particle size analysis was performed using Model ELSZ-1000. Zeta potential was analyzed using Model ELSZ Neo to confirm the cohesiveness of SS. In the case of the small particle size group, the D₅₀ value of the YD was 4.15 μm, which was larger than that of HB (average 0.95 μm) and HT (average 2.70 μm). The small particle size group was applied because it did not have aggregation during storage after sampling. During the column experiment, the boundary surface of the SS was distinct only at YD, which had the highest SS concentrations. The settling rates of the SS for YD, HB, and HT were about 7.0, 0.048, and 1.11 cm/min, respectively. Moreover, zeta potential values of YD, HB, and HT were +1.8 mV, -16.3 mV, and -10.1 mV, respectively.

The zeta potential near zero may have been favorable for larger floc sizes. Also, hydrated lime for pH adjustment was applied for YD and HT facilities, which led to coagulation effect. Thus, higher settling rate was resulted from zeta potential near zero and larger particle diameter.

Water resources have become a serious environmental issue, and the main concern is ensuring water availability and quality for different purposes. Uranium mines are often associated with releasing Potentially Toxic Elements (PTE) in water and sediments. Stream sediments have an essential role in contaminant retention processes. Therefore, stream sediments are considered a good water quality indicator. Also, the partition coefficient (Kd) is a valuable parameter to determine the behavior of PTE in a water environment, reflecting the mobility between water and solid phase in the water-sediment system.

A U-mine in Central Portugal was exploited in an open pit between 1987 and 1988, producing about 12430 kg of uranium oxide (U₃O₈). The mine is now abandoned, the rejected materials (1 million tons) were deposited in two dumps, and a lake was formed in the open pit. A total of 20 stream sediment and water samples were collected in a hydrological year to analyze water-sediment interaction in this post-mining U-mine area. Physic-chemical parameters (pH, temperature, electrical conductivity (EC), redox potential, alkalinity, and Total Dissolved Solids) were measured in the field and PTE were determined by ICP-OES at the University of Coimbra (Portugal).

Most stream sediment samples have a pH value varying from 4.4 to 6.4 and EC from 13 to 154 µS/cm. Waters are near neutral (pH: 6.2-7.2) and poorly mineralized (EC: 58-111 µS/cm; TDS: 58-111 mg/L) with low metal concentrations (S_{Zn+Cu+Cd+Ni+Co+Pb}:322-602 µg/L). No relevant difference exists between the chemical composition of the stream sediments and waters collected outside and inside the mine influence. The partition coefficient between stream sediments and water ranges from 2.42-3.18 kg/L for Th, which is lower than the mean value (Kd=2.5 kg/L) indicated by IAEA (2010), suggesting that Th has more affinity to be in solution (Th water concentration: 0.015-0.044 mg/L). Otherwise, the Kd values for U (2.43-4.20 kg/L) and for As (2.27-3.11 kg/L) indicate that these elements tend to be absorbed on complex phases of stream sediments, which could be suggested by the low variability of U and As water contents increasing distance from mine area (U: 0.070-0.084 mg/L; As 0.018-0.028 mg/L).

The results suggest that stream sediments are a water quality indicator and contribute to water management in abandoned mine areas. Therefore, further studies should focus on water-sediment interaction and mineral speciation modeling to identify functional processes for monitoring water quality.

Portugal and Spain are mining countries with a long tradition of exploiting metals in different metallogenic provinces. Consequently, signs of degradation are associated with abandoned mining works crossing several regions in SW Europe, like the Iberian Pyrite Belt (IPB). Mine waters are usually the focus of environmental problems, with no borders on river contamination and habitat destruction. The present study reveals the influence of ore deposit type, paragenetic, and climate diversity on hydrochemistry, contamination, and nature of associated precipitates found in different mining sites.

To understand the spatial distribution, seasonal behavior, and relationships of pollutants in affected streams, three mining areas with different geographic, climate, paragenetic, and rehabilitation states were selected: Valdarcas (W mine in a skarn deposit, northern Portugal); São Domingos (massive sulfides in the Portuguese sector of the IPB); and Campanario, (Cu in the Spanish sector of the IPB). Sampling occurred during a hydrological year, measuring in situ parameters (pH, electrical conductivity (EC), redox potential (Eh), and temperature). Samples were collected for sulfate, acidity/alkalinity, and metal(lois) analyses. At each sampling site, filtered (< 0.2 µm) and unfiltered samples were prepared to compare dissolved and total concentrations. Supergenic products, such as ochre precipitates and salt efflorescences associated with these waters, were also collected and analyzed for chemistry and mineralogy.

Results differentiate between the three sites' regional backgrounds and mine-influenced waters. pH, EC, Eh, acidity, and sulfate indicate high aquatic ecosystem degradation in São Domingos mine. The effect of natural attenuation is also verified, especially by dilution and precipitation. Eh values agree with the concentration of iron(III) and iron(II) related to oxidation-reduction reactions. Different contamination ranges can be observed, with Ficklin diagram giving high-acid, acid, and high-metal or low-metal classifications.

Although there are different climates and AMD sources in the three sites, the relationships between indicators are similar. Nevertheless, the magnitude of contamination is different. Seasonal variation is more pronounced in Valdarcas, related to climate variety and rainy periods. Also, the presence of carbonates promotes neutralization reactions with the precipitation of ochre products. However, this is not enough to avoid contamination by AMD, with a pH of around 3. This study illustrates the need for efficient monitoring and remediation protocols, even in sites already submitted to rehabilitation.

Converting former coal mining and industrial sites into hubs for new economic activities is a complex endeavor, marked by numerous challenges. To address these challenges, the CoalHeritage initiative, part of the Conservation and promotion of the Coal Mining Heritage as the EU's cultural legacy, has been established as an RFCS accompanying measure.

The primary objective of CoalHeritage is to establish a robust interregional network dedicated to the preservation and promotion of coal-mining heritage in post-mining regions. The network's approach encompasses the identification, inventory, and valorization of assets from selected coal mines. Building upon these foundations, a comprehensive strategy for their conservation will be developed, incorporating best practices and outlining the processes necessary for declaring a coal mine as a national heritage.

Within the scope of this contribution, we aim to showcase the ongoing structural transformations associated with the German coal phase-out, including the evolving legislative landscape and socio-economic strategies geared towards the reactivation and transition of post-mining areas. Additionally, we will conduct an in-depth analysis of stakeholder engagement and involvement.

The ultimate goal is to integrate all the findings into the European Visual Map Journal (EVMJ), with the intention of fostering collaboration with other industrial heritage networks. This collaborative effort seeks to amass knowledge, build relationships, and expand the initiative's reach to include additional sites. By doing so, we strive to promote the overarching goals of the CoalHeritage project and secure maximum engagement and consultation with stakeholders.

Germany and many parts of the world were shaped by mining for centuries. These abandoned mines have a considerable potential as a source of energy and raw materials and offer a wide range of energy storage options. These energy storage facilities can highly contribute to a renewable heating and cooling system in buildings. Especially Aquifer thermal energy storages (ATES) are appropriate options, especially for an intermediate storage of seasonal energy surpluses from fluctuating renewable energies and waste heat, e.g., from industrial plants. The project "MineATES" is investigating various base-load supply options for buildings and quarters using aquifer heat storages. Simultaneously, sub-surface tests for three real-lab sites in Germany are carried out to determine criteria for feasible ATES energy supply options.

The novelty is the development of a fully automated model using spatial data, which systematically records potential heat sources and performs site-specific analysis to calculate the storable thermal energy potentials considering waste heat, solar thermal applications and other fluctuating renewable energies. The model includes an interface to use measured site-specific storage efficiencies and heat losses to analyze ATES storages in different scenarios and locations. Thereby, storage load cycles and consumer load profiles are considered to estimate the energy dissipation in the quarter supply. Additionally, the heat production costs for various supply options will be estimated.

The core result of the project is a criteria catalogue evaluating the suitability of ATES systems in heat supply concepts at locations worldwide based on the GIS-simulations and real-lab tests. Initial results at the real-lab site in Freiberg/Saxony show that the inclusion of waste heat sources in supply concepts with ATES systems are essential to guarantee the economic feasibility. In particular, the storage of solar thermal energy, but also electricity from wind and PV which is not fed into the grid from ground-mounted systems as well as industrial waste heat enable a base-load capable supply. Furthermore, especially the combination with an anergy supply network is highly feasible and economically suitable.

Considering legal requirements, the project "MineATES" yields in various criteria for the development of future ATES-systems. This will leverage ATES-based systems based on scientifically developed criteria which can be used from planning- and implementing institutions. Thus, for regions that have the possibility to establish ATES systems, tangible recommendations for a innovative renewable and base-load-capable heat supply will be shown. Leveraging the project's influence, the German Upper Mining Authority is already involved as a partner.

This paper addresses critical environmental, health, regulatory, and scientific concerns related to gold mining activities in the specific area of Barberton, Mpumalanga, South Africa. The paper thus calls for informed decisions to be made by the authorities to safeguard both the environment and people’s health.

The novelty of this study is based on its comprehensive nature of the simultaneous assessment of both cyanide and potential toxic elements (PTEs) in tailings, while taking into account their composition variability over time. By combining these aspects, it is then possible to provide a holistic understanding of the contamination risks associated with mining tailings and thus justify the need for regular monitoring and supervision to ensure compliance against regulatory limits. Additionally, this paper considered investigating the dynamic nature of tailings, which are subject to changes in their chemical composition due to exposure to weathering by various agents.

In this study, the determination of weak acid dissociable (WAD) and free cyanide in tailings was performed using a validated method employing the South African Council for Mineral Technology (MINTEK) Laboratory Cynoprobe. The PTEs in tailings were determined by an inductively coupled plasma optical emission spectrometer (ICP-OES).

The results revealed that the tailings contained primarily substantial amounts of PTEs, including Fe (87,566 to 37,800 mg/L), Cu (271 to 110 mg/L), Mn (2,100 to 680 mg/L), Ni (400 to 390 mg/L), Zn (180 to 68 mg/L), Cr (645 to 510 mg/L), As (450 to 128 mg/L), and Pb (up to 35 mg/L).

The cyanide concentrations in tailings varied between 0.20 mg/L and 0.26 mg/L for free CN (with a mean of 0.23 mg/L in water leaching), 0.23 mg/L to 0.28 mg/L for free CN (with a mean of 0.25 mg/L in alkali leaching), 0.24 mg/L to 0.35 mg/L for WAD CN (with a mean of 0.28 mg/L in water leaching), and 0.31 mg/L to 0.39 mg/L for WAD CN (with a mean of 0.35 mg/L in alkali leaching).

The measured concentration of cyanide and the PTEs was compared to the minimum permissible levels enforced by the South African Department of Water and Sanitation (DWS) and the Water Research Commission (WRC) regulations that govern the disposal of hazardous constituents into the environment. Additionally, it was observed that the concentrations of contaminants in the tailings exceeded the acceptable minimum limits for hazardous waste exposure, posing risks to the environment and human health.

Given the importance of dewatering processes to the question of water recovery (and therefore closed water circuit design) and tailings management, concentrators are putting in many interventions into ensuring that dewatering processes are designed and operated with maximum efficiency. This means that interventions such as the addition of dewatering chemical agents are added to dewatering unit processes in order to improve the efficacy of dewatering. These chemical agents often come in the form of flocculants and coagulants. Their effects on flotation are not well understood, this begs the question, how will residual flocculants and coagulants in recirculated process water affect flotation performance. This study therefore investigates the adsorption of CMC as a depressing reagent for talc in process water that contains residual flocculants and coagulants. The results of this investigation showed that process water containing residual concentrations of the coagulant resulted in higher CMC-talc adherence. It was also shown that the zeta potential of talc increased (became more positive) in process water containing the flocculant – indicating a passivation mechanism.

Upstream-Constructed Coal Refuse Impoundments have unique characteristics as compared to the other engineering structures as the hydraulically-deposited fine coal refuse (FCR) is used as the foundation material. Key design aspects for such structures include developing and implementing risk-appropriate in-situ field and laboratory testing, characterizing embankment and foundation materials, and the FCR material. FCR in particular requires comprehensive evaluation of the physical properties, undrained shear strength, seepage and settlement parameters. These parameters are then used to analyze the stability during construction and determine the rate of placement/loading Coarse Coal Refuse (CCR) material on top of the FCR without compromising the stability of the system.

Information to develop the site exploration program for upstream-constructed coal refuse impoundments, and key elements required for site characterization. Cone penetration testing (CPT), and CPT data variations for different materials (depending on their behavior)and the the use of seismic CPT with pore pressure measurement (SCPTu) for upstream construction are key.. The pore pressure dissipation data obtained from SCPTu can be interpreted to obtain the estimates of groundwater conditions, and seepage properties, particularly permeability and consolidation characteristics. How CPT data can be incorporated into the analyses will be discussed.

A case study is presented in which the required strength of the FCR is determined using the stability analysis to achieve the short-term factor of safety of 1.3. This strength is then compared with the strength gained by the FCR material for different construction/loading rates. Once the loading rate is established, and placement of the fill starts, the next step is monitoring the response of the FCR material to ensure consistency with the assumptions made in the analyses. This is achieved by installing rapid response piezometers at strategic locations, and monitoring the excess pore pressures developed during construction. Action levels are developed for monitoring of the piezometers, which indicate the system will remain stable (having factor of safety of 1.3 or greater) as long as the excess pore pressure readings from installed piezometers are below the action levels. The monitoring of the pore pressures from the same case study as discussed above will also be presented and compared to the action levels.

In conclusion, this paper presents the details of upstream-constructed coal refuse impoundments, developing the investigation plan for site characterization for such impoundments including effective use of SCPTu data for loading rate analyses, and effective monitoring of the performance of the system.

Polluted mine water is treated using active and passive treatment systems. Active systems require electrically powered equipment, chemicals, and regular maintenance to treat polluted mine water. Whereas, passive systems depend on naturally occurring biological, geochemical, and physical processes to treat polluted mine water. Passive systems are preferred over active systems because of their cost-effectiveness. These systems typically use natural construction materials (soil and rocks), and natural treatment materials (wood chips, limestone, compost). Furthermore, they rely on gravity for water flow, and aesthetically, they can be integrated into the natural landscape, and they usually have a longer lifespan. The use of passive treatment techniques to treat mine drainage (AMD) is well documented all over the world. One such technique is the reducing and alkalinity-producing system (RAPS), which combines bio-geo-chemical and physical processes to treat AMD through neutralisation and bacterial sulfate reduction. The setup of the system is a combination of the anoxic limestone drain (ALD) and anaerobic wetland systems. In this system, acidic water is ponded from 1 – 3m over a 0.2 – 0.3m layer of organic compost substrate which is underlain by a 0.5 – 1m layer of limestone aggregates. The compost is a source of sulfate-reducing bacteria (SRB) providing anaerobic conditions and is responsible for sulfate reduction and precipitation of metals. The limestone layer is responsible for generating alkalinity and metal removal by raising the pH of the system. The system typically operates as a downward flow reactor in which water flows from the top of the system to the bottom. Treatment occurs as the water percolates downwards through the treatment material (compost and limestone) and is eventually discharged through pipes. In this review, RAPS will be discussed in detail with an aim to propose ways in which its efficiency, performance and longevity for polluted mine water remediation can be improved or optimized in South Africa. Furthermore, the processes involved in the treatment, limitations and advantages will be explored.

The importance of this research lies in addressing the issue of legacy mine drainage treatment in Japan. With over 70 legacy mines involved in mine drainage treatment, the burden falls on local authorities due to the absence of responsible parties. These operations have been consuming approximately 13.4 million USD annually over the past five decades. Sustainable mine drainage management is essential not only for environmental protection but also for its significant economic effectiveness.
This study introduces an approach to assess and prioritize two national measures promoted in Japan for mine drainage management: passive treatment (PT) and point-of-use management. PT involves cost-effective methods utilizing natural biological and physiochemical reactions (Fe-oxidizing bacteria and artificial wetland), while point-of-use management sets site-specific water quality benchmarks to maintain river water quality downstream of mine discharges. The research evaluated the applicability of these measures to 26 legacy mine drainage systems, ranking them based on their suitability to strategically optimize mine drainage management. The applicability of the PT was evaluated using a 5-year dataset of mine water chemistry (dissolved Cd, Pb, As, Cu, Zn, Mn, and total Fe concentrations and pH) and flow rate. Point-of-use management applicability was evaluated by estimating the metal concentrations downstream where untreated mine drainage was discharged.
The main findings of this study revealed that passive treatment (PT) could be effectively applied to 14 mine drainages with Cd, Pb, Cu, and Zn concentrations (<10 mg/L) and flow rates (0.5 m³/min). However, it was not suitable for 10 mine drainages due to extreme total Fe concentrations. Point-of-use management, on the other hand, was applicable to 10 mine drainages as their estimated metal concentrations met downstream water quality standards, even without treatment. Combining either PT or point-of-use management allowed 23 mine drainages to potentially reduce costs by 4.4 million USD per year (33.4% of total costs). Nevertheless, for the remaining three mine drainages with excessive Fe concentrations, neither of these measures was applicable, resulting in an annual cost of 8.0 million USD (58% of the total costs).
Our study suggests that a dual strategy involving passive treatment and point-of-use management is effective in achieving sustainable mine drainage management for the majority of legacy mines. However, for the remaining three mine drainages, alternative approaches will be necessary to optimize their management and reduce costs. This research provides insights into the potential economic and environmental benefits of adopting these measures.

Why is this abstract important?

Abandoned mine pools (AMPs) result from groundwater rebounding after closure of mines that are below groundwater tables or under potentiometric pressure. They can encompass hundreds of square kilometers in extensively mined regions and are potential sources for underground water reservoirs, heat pump solutions for building heating and cooling, and threats to human health and the environment. Several case studies were summarized to present a working approach to minimize levels of threats from the AMPs while maximizing their potential for beneficial use.

What is novel in your approach; what was done?

AMPs are physically and hydraulically different from “typical” aquifers. Groundwater dynamics and geochemical evolution follow unique rules, and analyses using traditional methods present challenges. The experience and lessons learnt from the case studies demonstrate that the appropriate site characterization and mitigation methods depend on the development of representative conceptual site models (CSMs). Based on the data from groundwater level and discharge monitoring, geochemical analysis, isotopic fingerprinting, tracer testing, and beneficial uses of the AMPs, site-specific CSMs were generalized and included not only the recharge sources, mine workings, and pathways from recharge through the AMPs to receptors, but also the hydrogeological, geochemical, biological, and geotechnical attributes and the interactions between these attributes.

What are your main findings?

To maximize the potential for beneficial use and minimize levels of the threats of any AMP, the CSM is a necessity and must address the specific characteristics of the AMP and the purpose for the study. For AMPs that cause safety concerns, the hydrogeological and geotechnical conditions are critical components in the CSMs, while for AMPs containing low pH and high concentration of metals, pollution is a concern, and the hydrogeological, geochemical, and biological conditions are important components.

What are the main applications and implications of your work?

Development of CSMs is a critical step to determining the nature and extent of the AMP and evaluating the feasibility of beneficial uses, risk to human health and the environment, and remedies to mitigate any unacceptable risks. The CSM is site-specific and iterative depending on the data available. The CSMs developed from the case studies provide examples that are useful for site characterization and mitigation of AMPs that are globally distributed.

Mining exploitations represent a serious problem of environmental contamination. One example is sulfide extraction, associated with deposits of metals and coal that generate large amounts of waste, typically stored in piles around the mine. Although, the major problem is related to the weathering processes. In this situation, complete degradation of the ecosystem may occur due to acid mine drainage (AMD). Knowledge about the properties of different types of waste and their spatial distribution is crucial to evaluating the evolution of contamination by AMD.

The work aims to present a mapping procedure for the mining waste accumulations at the São Domingos mine, which closed in 1966 without remediation measures. It is in the Iberian Pyrite Belt, known as one of the biggest metallogenic provinces in the world. The composition of wastes, namely the amount and type of sulfides, can control the waste reactivity, here expressed through the paste pH. So, this novel approach allows an expeditious classification of waste accumulation areas based on paste pH. The mapping defines areas with reactivity indices that vary from non-reactive (paste pH >5) to very reactive (paste pH <3). In addition, water was sampled in a complete hydrological year, contemplating two water courses draining the mining complex.

The main result is a map of the entire mining area with different colors representing different types of wastes from different exploitation periods (from Roman to modern times) and ore deposit paragenesis. There is a total waste area of 145 ha. The most suggestive contaminating potential was detected in the North sector (near the pit lake) and the industrial zone, which is very reactive. These align with the results obtained for hydrochemistry in surrounding sections of the aquatic system, with a minimum pH of 0.40 and a maximum sulfate of 410601 mg/L.

There is a direct relation between the properties of the wastes, expressed by their reactivity, and the water hydrochemistry. Thus, the waste paste pH can be considered an indicator of the contamination degree as the lowest paste pH (highest reactivity) corresponds to the lowest water pH in the river system (worst water quality). Water resources management and environmental protection measures are essential in a climate change scenario. So, this work intends to contribute in-depth knowledge of an issue known to affect worldwide and assist the competent authorities in implementing best practices for environmental protection.