Post-mining Period Research Articles

Engagement strategies in the context of the Itabira mine closure: impacts and stakeholder participation

Purpose: This article aims to propose and apply a set of analytical categories for evaluating engagement in mine closure processes. Design/methodology/approach: The qualitative research adopts a case study strategy considering the singularity of the phenomenon studied. The mine project analyzed is the country's first large-scale closure, scheduled for 2041, with the potential to influence future processes. Data collection involved observation, documentary analysis, and interviews. Sixteen interviews were conducted with representatives from the public power, community, organizations, and the company. The research strategy chosen was content analysis using the analytical categories raised in the literature review and triangulation of data collection sources. Findings: The results highlight the importance of the mining company's active role in constructing the city's post-mining future, collaborating to reconvert socio-economic dynamics, and fostering a trusting relationship with the community. However, the company remains distant from the debate. Interviews revealed a paternalistic relationship between the mining company that guides engagement in a predominantly unilateral flow, with communication directed to meet its interests. Originality/value: This research fills a gap in the existing literature by focusing on engagement in a vulnerable context. It contributes to the theoretical advancement of the main characteristics of engagement in mine closure processes and for dialogue practices with communities to favor sustainable territory development in the post-mining period.

Post-Mining Multi-Hazard Assessment for Sustainable Development

Today, most mines (coal, iron, and others) in Europe are already closed due to economic, environmental, and societal issues. Therefore, post-mining risk assessment and management remain crucial for mining authorities, policymakers, and planners. In the post-mining period, several hazards are likely to affect the surface areas in the closed mining sites. The impact of closed mines can lead to potentially damaging changes in surface and/or underground water flow, as well as the development of surface instabilities that can affect people or infrastructure, sometimes dangerously. The assessment of the different hazards must consider the interaction between the mining hazards and other risks (natural and technological). Thus, land use planning, particularly the rehabilitation of former mining sites, requires better tools to apprehend the multiplicity of hazards and their constraints. The paper presents a methodology considering the interactions between hazards around closed mines. After recalling the advantages of this multi-hazard analysis, the work consisted of, almost exhaustively, describing the three prominent families of hazards: mining, natural, and technological. Then, the possible interactions between hazards were described according to their nature (trigger or aggravating), their category (technical or regulatory), and their typology (dependent or independent). Finally, an attempt was proposed to evaluate the type and intensity of interactions between hazards. The multi-hazard assessment methodology was applied to a coal mine and showed the complexity and the utility of such a risk assessment analysis to improve risk management in closed mines.

Quantifying the coal mining impact on the ecological environment of Gobi open-pit mines

Xinjiang is a coal-rich region with many bare rocky and gravelly areas with a delicate and fragile ecology. What is the ecological impact of mining activities? In this study, the Salinity Index (SI-T), New Gravel Land Index (NGLI), and Land Deterioration Index (LD) were used to establish an improved remote sensing ecological index (IRSEI) for the HongShaQuan open-pit coal mine (HSQ). The spatial and temporal evolution of the ecological environment of the HSQ was revealed by IRSEI and unary linear regression analysis. Moreover, the influence of mining on the ecological environment of the Gobi mining area was quantitatively evaluated by the random forest model (RF) and difference-in-difference (DID) approach. The results indicated that the value of IRSEI in HSQ had typically decreased over the last 30a. The ecological environment in most areas of the study area was poor and fair levels. The ecological environment of the whole study area showed a decreasing pattern from southeast to northwest. The proportion of degraded area (52.33 %) was much higher than that of improved area (0.39 %). The average residual before and after mining in HSQ were -0.1011 and -0.2323, respectively, which were much higher than that of the whole study area (‐0.0330 and -0.0658, respectively), indicating that the mining activities in HSQ harmed the ecological environment and aggravated the degradation of the ecological environment. The impact of mining activities on the ecological environment from 2000 to 2021 was ‐0.138 using DID. The results from the multiple regression model (MR), RF, and DID during the pre-mining period (2000−2011) were -0.0709, -0.1011, and -0.1345, respectively, while they became -0.1765, -0.2323, and -0.1963 during the post-mining period (2012−2020), respectively. The latter was worse than the former, all showing that the mining activities of HSQ had resulted in a negative effect on the ecological environment. It also demonstrated that the negative value of mining from the MR, RF, and DID have a very similar change trend and was near in value. This verified the feasibility of DID and RF in quantitative analysis of the ecological environment. The ecological environment quality of HSQ was mainly affected by climate change, and less influenced by mining, the contribution rates of both in the IRSEI improved area were 88.48 % and 11.52 %, respectively; and in the degraded area were 69.45 % and 30.55 %, respectively. Therefore, the Gobi mining area should pay attention to the protection of the ecosystem while developing coal. Planting vegetation can promote the governance and restoration of the ecological environment in the mining area.

Semi-real time systems for subsidence monitoring in areas affected by underground mining: the example of the Nuraxi-Figus coal district (Sardinia, Italy)

Underground mining can produce subsidence, which can be coincident with mining activities or delayed in response to the time-dependent deformation of the rocks. Therefore, in these cases, it is essential to effectively monitor the soil deformations at different times during and after mining activity. In the present work, an integrated approach based on geotechnical numerical modeling and Advanced Differential Interferometric Synthetic Aperture Radar (A-DInSAR) method has been applied to detect, study and monitor the subsidence related to mining activity in the Nuraxi Figus coal district (Sardinia, Italy). Two datasets of high-resolution COSMO-Skymed images were acquired, respectively in two covering periods: from 2011 and 2014, and from 2013 to 2020. The A-DInSAR results show that the predominant displacement rates are located in correspondence with the panels. The cumulated satellite-based LoS displacements vary in the first period between − 130 and + 28 mm and − 293 and + 28.4 mm, while, during the second period between − 6.9 and + 1.6 mm and − 8.72 and + 4.33 mm in ascending and descending geometries, respectively. The geotechnical numerical model allowed to obtain a value for the maximum expected. By using the vertical and horizontal components it was possible to reconstruct the kinematics of the deformation considering three phases: pre-mining, syn-mining, and post-mining activity. The temporal evolution of displacements started during the mining extraction in 2011, achieved the major values in correspondence of post-mining operations, during the period from 2013 to 2014 and continued slowly until 2020. The near real-time monitoring system applied in this study proved to be very useful for detecting subsidence during the mining activity and the post-mining period.

Laboratory Simulation for Reducing Water Turbidity by Water Hyacinth to Meet Coal Wastewater Discharge in Paringin Pit Lake

Coal mining with an open-pit mining method can created the formation of pit lake filled with high turbidity water which has the potential to pollute and cannot be utilized if not managed properly. Treatment to reduce water turbidity to meet quality standards with chemicals is a common, but during post mining period, it is necessary to reduce the processing, which is expensive and uncertain, turning into a natural process and lower cost. The aim of this study is to analysis on the role of water hyacinth as macrophytes in reducing water turbidity on three different water sources for treatment. Water hyacinth is an aquatic plant that can be used to reduce water pollution such as high levels of turbidity in water quality. The experimental results showed that not significant on TSS < 200 mgL-1 but significantly different results, on TSS values between 200 - 400 mgL-1 and TSS > 400 mgL-1 and to be the basic reference data of the number of plants used in experiment to enlarge it on a field scale

Time evolution of mining-related residual subsidence monitored over a 24-year period using InSAR in southern Alsace, France

From 1910 to 2002, the Mines Domaniales de Potasse d’Alsace (MDPA) exploited two potash layers, located at depths greater than 400 m in the southern Upper Rhine Graben. This mining activity has caused surface subsidence, investigated here using SAR interferometry (InSAR) and Persistent Scatterer Interferometry (PSI) approach is used to follow mining induced surface displacements over the Alsatian potassic basin. The SAR images acquired by three distinct satellites (ERS, ENVISAT, Sentinel-1) over the last 24 years cover both mining and post-mining periods. Until 1996/1997, InSAR results do not fit the high vertical displacement deduced from levelling campaigns due to unwrapping errors and are therefore not reliable to quantify the mining subsidence. From 1996/1997, InSAR results and levelling measurements become consistent, allowing us to study the subsidence following the activity of the mine. The surface subsidence decreases quickly after the end of mining operations, with current subsidence estimated below 5 mm/yr in 2018. The InSAR results obtained for the post-mining period show a correlation between residual subsidence amplitude and the mined thickness. Taking together the InSAR and levelling measurements for the whole 24 years period, the combined time series are approximated by a sum of two exponential terms, which reveals the role of the goaf compaction at depth. The study shows that SAR interferometry is well suited for monitoring small amplitude mining-induced subsidence over the residual phase, helping to better mitigate the related risk in these regions.

Study of rare earth elements potential in acid mine drainage from coal mine: a case study

Acid Mine Drainage (AMD) is one of the crucial impacts of coal mining activities. This issue is becoming increasingly important because acid mine drainage will become a burden in the post-mining period if not appropriately managed. AMD can leach side materials, causing an increase in dissolved heavy metals, including Rare Earth Elements. REE is an essential raw material for applying modern technology whose demand is increasing globally from year to year. Until 2019, 77% of REE production came from China. The combination of scarce supply and high demand has encouraged various studies to evaluate alternative REE resources. In Indonesia, there is few research about the presence of REE in AMD from coal mine. The objective of this study to determine the amount, characteristics and enrichment mechanisms of REE in AMD, moreover this research is a preliminary study on the alternatives of REE resources. Five water samples were subjected to physical tests well as analysis of IC and ICP-MS. The water sample was 5 had a low pH of 2.90 - 3.82. The concentration of Total REE (not include Lu and Tb) from samples ranged from 0.1032 - 0.6174 ppm with an average Total REE of 0.4810−3 ppm.

Miner Artist/Minor Artist? Class, Politics, and the Post-industrial Consumption of Mining Art

This article uses the recently discovered art work of a County Durham coal miner, Jimmy Kays (1886–1951) to highlight the terms in which coal mining art has achieved popularity and value in the post-mining period. Kays' work is considered with reference to the presenting narrative that promotes and markets mining art not only in terms of its intrinsic artistic quality, but also as a desirable commodity which, as a legacy of the mining past, can contribute to the revival of post-mining places. Maximizing the value that can accrue from mining art in post-industrial conditions involves appealing to the interest of the largest possible audience. The consequence of this is the dominance of a particular interpretation of the mining past. The art of Jimmy Kays does not conform to the conditions of the market, and cannot achieve a similar status. Despite its artistic qualities and its uniqueness as the product of a Durham working miner in the early twentieth century, it sits outside the dominant lexicon of coal mining art. The outsider status of Jimmy Kays is an example of a wider set of issues relating to the invisibility of working class creativity and the difficulties of achieving excellence or public acknowledgment in conditions that lack organizational support and in which value is established elsewhere. I argue that an understanding of the invisibility of art work such as that produced by Kays illuminates the exercise of class-based power in terms of the production, consumption, and range of meaning inscribed within popular mining art. Mining art that has been allocated value is in danger of being appropriated in ways that pacify rather than energize audiences, by foregrounding particular aspects of the mining past for purposes of consumption whilst submerging the issues that link more troubled aspects of the past with the present.

Numerical analysis and prediction of ground surface movement induced by coal mining and subsequent groundwater flooding

Ground surface movement shows different features during mining and post-mining period. If the mine goaf is dry, surface subsidence is observed in both periods. If the mine goaf is flooded by groundwater, however, ground surface uplift can be observed although much smaller in amplitude compared to the preceding subsidence. A numerical modeling strategy is proposed to predict uplift during the flooding process of an excavated coal mining area under complex geological conditions. The modeling approach considers three phases: virgin state before mining, stage immediately after mine closure, flooding phase. The model considers elasto-plastic material behavior including faults represented by interfaces. In-situ measurements are used for calibration of the model. The Oelsnitz abandoned coal mine is used for model validation and prediction. The measured subsidences up to 17 m were reproduced as well as the uplift within the last 10 years with values between 0.5–2.0 mm/year. Spatial distribution of uplift areas is well reproduced. Predictions up to the year 2051 show an increase in uplift velocity between 0.5–3.0 mm/year and additional total uplift of up to 300 mm.

Monitoring of the condition subsurface on the post mining period in the Ural region (Degtyarskiy land area)

Objective of the work: to study the state of the territory of Degtyarskiy area during the period of mining postexploitation and to study the methods for assessing and taking into account the current state of this object. Relevance of the topic. The postmining land area is the territory of mining development, including disturbed and under-worked land, where mining production is currently stopped and a certain amount of reclamation activities are implemented. According to numerous Ural’s data, hazardous geological processes are being activated in such land areas, so the Degtyarskiy section has been used as part of the state monitoring of the condition subsurface. The article presents the research methodology implemented over the past 10 years, and discusses the results obtained (as of 2019). Methods of investigation. For assessment of subsoil in Degtyarskiy phase, in addition to the analysis of the prior information, conducted periodic visits to the site from visual observations with photographic documentation, including remote shooting of the territory; bathymetric plots areas of the mine water output (quarry excavation) and dentinho target (Elchevsky pond-sump); serial sampling of water and bottom sediments in the control hydro sections; measurement of the hydrogen index of the aquatic environment at the site; laboratory testing of samples for specific components of specific chemical composition. The results of the work. According to obtained materials, dangerous level of the geochemical, hydro-and geodynamic disequilibrium is recorded at the Degtyarskiy post-exploitation site. It is proposed to continue periodic observations on the site as analog object, uncluding the works of both remode and geochemical nature in the mode at least once every five years. Conclusions. According to the set of indicators, the post-exploitation site is proposed to be classified as a dangerous natural and man-made object, so it is recommended to create registers and passports for all Ural’s postmining sites.

Processes of hydrosphere self-rehabilitation and mine water treatment in post mining period

The hydrosphere of catchments, which are disturbed by mining, is formed under the influence of not only natural, but also, to a large extent, man-made factors over a long period, sometimes tens or even hundreds of years. After the cessation of production, the return of the mining territory to a state as close to natural as possible is possible, as world experience shows, in exceptional cases, provided that the process of reclamation and revitalization is planned at the design stage of mining. In old industrial areas, the selfhealing processes of the hydrosphere are of great importance, which determine the time during which the territory should be considered as an object of accumulated environmental damage. At present, the total removal of metal compounds by mine waters in the discharge zones at flooded copper-ore mines of the Sverdlovsk region amounts to hundreds (manganese, zinc) and even thousands of tons per year (iron). The duration of self-rehabilitation of the hydrosphere of mining areas at the post-operational stage, i.e. the duration of the period during which the content of the main polluting components (copper, zinc, iron, sulfate ion) is reduced to the maximum permissible or background values, is tens or even hundreds of years. During this time, in order to prevent pollution of the underground and surface hydrosphere, expensive measures are required to implement a system of purification of underground and surface waters of the old industrial territory. The research was carried out on the basis of observations of the chemical composition of water bodies in the territory of the abandoned Levikhinsky mine since the beginning of the 2000s.

The attractiveness of a post-mining city as a tourist destination from the perspective of visitors: a study of Sawahlunto old coal mining town in Indonesia

Mining has been a basis of development for industrial societies. A mining city was an engine of economic growth for a region by providing employment and gaining revenue from the mining industry. Nevertheless, in the post-mining period, a city such as this suffers from a lot of problems inherited from the mining era, ranging from economic incapability, social structure change, and environmental degradation. Transforming mining-heritage values for tourism applications has become a prevalent choice for many post-mining cities around the world. The attractiveness of mining-related resources is one of the determinants in the success of tourism development in these cities. This study measures the attractiveness of tourism resources within a smaller post-mining city from the perspective of the visitors. Twenty-two types of resources are identified and categorized into three groups: core resources, created resources, and supporting resources. Questionnaire surveys were distributed to 100 random visitors in Sawahlunto, an old coal mining city in Indonesia. Using a five-point Likert scale, these measured the levels of attractiveness respondents had for each resource. Study results reveal that natural beauty, mining heritage sites, museums, and architectural features are the most attractive resources found in a post-mining city by visitors. These resources become the primary motivation for their visit. It also confirms that visitors will likely arrange return trips in the future.

Utilization Study of Void Mine For Sustainable Environment of The Limestone Mining Sector at PT Semen Baturaja (Persero) Tbk

Event open-pit mining methods in the exploitation of limestone by PT Semen Baturaja (Persero) Tbk cause depletion of water, air, and soil. At the end of mining activities will leave ex-mine land in the form of void and non void (empty land). Reclamation and Postmining must be carried out by the company according to the mandate of Government Regulation No. 78 year 2010. Reclamation and post-harvest activities on ex-non void mines can be revegetation activities, while void can be used as reservoirs for raw water sources. The aim is to maintain the sustainability of natural resources and water in the limestone mining environment. The research aims to determine the condition of void water produced from limestone mining activities for a sustainable environment. The method used in this study is using the pollution index method. The results showed that the water in the sump inlet and quarry outlet experienced mild pollution. Pollution index at the location of the limestone mine sump inlet worth 2.14 and for oulet quarry worth 2.07. This shows that mine void water is not feasible to be used as raw water, so water treatment needs to be done so that it meets the established quality standards. If void water comply the prescribed quality standards, environmental sustainability in the limestone mining sector can be achieved during during the life of the mine, post mining, until after the post-mining period.

Evolution of Secondary Deformations Captured by Satellite Radar Interferometry: Case Study of an Abandoned Coal Basin in SW Poland

The issue of monitoring surface motions in post-mining areas in Europe is important due to the fact that a significant number of post-mining areas lie in highly-urbanized and densely-populated regions. Examples can be found in: Belgium, the Czech Republic, France, Germany, the Netherlands, Spain, the United Kingdom, as well as the subject of this study, the Polish Walbrzych Hard Coal Basin. Studies of abandoned coal fields show that surface deformations in post-mining areas occur even several dozen years after the end of underground coal extraction, posing a threat to new development of these areas. In the case of the Walbrzych area, fragmentary, geodetic measurements indicate activity of the surface in the post-mining period (from 1995 onward). In this work, we aimed at determining the evolution of surface deformations in time during the first 15 years after the end of mining, i.e., the 1995–2010 period using ERS 1/2 and Envisat satellite radar data. Satellite radar data from European Space Agency missions are the only source of information on historical surface movements and provide spatial coverage of the entirety of the coal fields. In addition, we attempted to analyze the relationship of the ground deformations with hydrogeological changes and geological and mining data. Three distinct stages of ground movements were identified in the study. The ground motions (LOS (Line Of Sight)) determined with the PSInSAR (Persistent Scatterer Interferometry) method indicate uplift of the surface of up to +8 mm/a in the first period (until 2002). The extent and rate of this motion was congruent with the process of underground water table restoration in separate water basins associated with three neighboring coal fields. In the second period, after the stabilization of the underground water table, the surface remained active, as indicated by local subsidence (up to −5 mm/a) and uplift (up to +5 mm/a) zones. We hypothesize that this surface activity is the result of ground reaction disturbed by long-term shallow and deep mining. The third stage is characterized by gradual stabilization and decreasing deformations of the surface. The results accentuate the complexity of ground motion processes in post-mining areas, the advantages of the satellite radar technique for historical studies, and provide information for authorities responsible for new development of such areas, e.g., regarding potential flood zones caused by restoration of groundwater table in subsided areas.

Technical analysis backfilling plans of integrated on post mining plan

PT Samantaka Batubara is one of the coal mining company geographically located in Kecamatan Peranap (Desa Pauh Ranap & Gumanti), Kecamatan Batang Peranap (Desa Punti Kayu), Kabupaten INHU of Provinsi Riau. Based on Minister of energy and mineral resources of the Republic Indonesia number 07 years 2014 on the reclamation and pascatambang, every mining industry must have post-mining planning to obtain mining operation. The objectives of research to know the direction of mining, the volume of pile plan and the design of the embankment. The study refers to the direction of mining from the beginning of 2017 from the southwest side to the end of the mine in 2022 to the northeast. The volume of overburden material stockpiles planned for the post-mining plan program is 2,500,850 LCM in the 1st in 2021 and 3,000,665 LCM periods of the 2nd in 2022 period. The backfilling design in this study follows the recommendation of geotechnical analysis with every 5 meter hump should be formed in a slope angle of 300, with the direction of the heap toward the east. Period prior to entering the post-mining program that is in 2017 the embankment forms the highest elevation of +83 whereas in 2018 to 2020 the highest elevation is flat at +63 elevation. Entering the post-mining period of the highest elevation plan established at +63 elevation in 2021 and 2022.

Tracking human impact in a mining landscape using lake sediments: A multi-proxy palaeolimnological study

Mining and metallurgy have caused vast devastation of the landscape in the past and left its legacy on terrestrial and aquatic ecosystems all over the world. Lake sediments provide a continuous record for tracking and better understanding of human-environment interactions related to historical mining and metallurgical activities. Here, we present the analysis of pollen, diatom, cladoceran and chironomid record combined with 210Pb dating, lithology and organic content of the sediments of Velka Richnava reservoir, located in an area intensively mined for polymetallic ores since the end of the 11th century (Banska Stiavnica region, Central Europe). Our aim was to reconstruct the changes in the vegetation cover in the catchment and aquatic biota initially caused by mining and after its cessation by changed management practices. Pollen analysis suggests an open landscape shaped by different land-use during and after the period of active mining toward increased grazing pressure and nutrient input and later to extensive urbanization and spontaneous tree and shrub succession on abandoned grasslands. Shifts in aquatic biota clearly distinguished the phase when the reservoir was used as hydraulic-power source for mining/metallurgy, characteristic by dynamic sedimentation and unstable hydrology from the post-mining period suggesting stabilized hydrology, developed littoral and nutrient enrichment, and later intense urbanization. Our study shows that sediments of man-made reservoirs have a great potential for palaeoecological reconstructions and can extend the current knowledge of past changes in mining landscapes that are rarely described in historical documents.

Long-term dispersal of heavy metals in a catchment affected by historic lead and zinc mining

The Matylda catchment, in southern Poland, was polluted by the discharge of mine waters from a lead and zinc mine that inundated parts of a valley floor and caused the accumulation of metal-polluted sediments. After a partial reclamation of the mine site in the early 1980s, polluted sediments continue to accumulate on downstream floodplains and in fishponds. The aim of this study was to reconstruct the changes in metal dispersal during 100 years of mining and during the 40-year post-mining period and to propose a strategy for pollution mitigation in the area. Analyses of Cu, Cd, Pb, Zn, Mn, Ca, Mg and Fe concentrations, speciation of heavy metals and mineralogical analyses were undertaken on overbank sediment cores and in stream sediments. Concentrations of the same elements and macro-ions soluble in stream waters were also determined. Concentrations of Zn, Cd and Pb in the sediment profiles vary between 40,000 and 55,000, 300 and 600 and 30,000 and 50,000 mg kg-1, respectively. Changes of metal concentrations and the stratigraphy of sediments from the floodplains, stream channels and fishponds suggest rapid changes of metal loads migrating downstream during both the mining and post-mining periods. Since the time of mine closure, fine-grained, mine-derived sediments (ca. 12 cm thick) have been the main source of pollution of post-mining sediments and surface waters. Closure of the mine was followed by a relatively short period of rapid redistribution of sediment-associated heavy metals in the stream channel. Since the 1980s, the floodplain and fishponds have received a constant supply of metals. It contrasts with the slow sediment accretion rate and a rapid decrease of metal concentrations in floodplain pools due to dilution by decomposed leaf litter. A fivefold increase of Cd content in waters over the 4.6 km reach of the Matylda stream indicates continuous leaching of this element from the contaminated valley floor. Unsuccessful mine site rehabilitation is due to leaching of mine-originated sediments dispersed over the valley bottom. However, the rate of metal remobilization over the last 40 years is low because of the small thickness and widespread anoxic conditions that prevail within both recent and mine-originated sediments and the alkaline pH of stream water, which reduces metal mobility. Distribution of the contaminated layer over a large area of the valley bottom precludes cost-efficient catchment rehabilitation.

Paleolimnological evidence of mining and demographic impacts on Lac Dauriat, Schefferville (subarctic Québec, Canada)

Qualitative and quantitative analysis of fossil diatoms and geochemical signals preserved in the sediments of Lac Dauriat (subarctic Quebec) were performed to evaluate the impacts of nearby mining activity and the expansion of the town of Schefferville on the water quality of the lake, and to reconstruct the changes of its trophic status. The presence of taxa typical of nutrient-enriched environments (e.g., Cyclostephanos invisitatus, Nitzschia gracilis, Nitzschia perminuta) and the low percentages of chrysophytes were indicative of the advanced state of eutrophication of the lake during the peak of mining activity, and were evidence of the negative impacts of municipal waste on the water quality of Lac Dauriat. Sedimentary analysis of metals, notably lead, mercury, cadmium, bismuth, cobalt, copper and zinc, showed maximum concentrations between 1940 and 1960 with mining era to pre-development enrichment factors ranging from 4.5 to 7.9. The changes seen in recent sediments reflected 3 distinct stages in the recent history of this ecosystem: (a) the non-perturbed, pre-mining (1882–1939), (b) the perturbed, mining period (1939–1977) with accelerated eutrophication, and (c) the post-mining period (1977–1999) with indications of natural recovery of the system after the installation of a water treatment plant in 1975, the closing of the mine in 1983, and the subsequent exodus of the town’s population. Despite the trajectory towards a return to the lake’s natural conditions, water resource managers and (paleo-)limnologists should be alarmed that the impacts of past human disturbance are still in evidence more than 20 years after the closure of the mines, and that Lac Dauriat has yet to reach its natural state of the period preceding extreme anthropogenic impact.

Hydrochemical models of the sulphidic tailings dumps at Matchless (Namibia) and Selebi-Phikwe (Botswana)

The sulphidic tailings dumps at Matchless (Namibia) and Selebi-Phikwe (Botswana) are located in a similar semiarid environment but have a contrasting mineralogical composition. The Matchless tailings are pyrite-rich, whereas the Selebi-Phikwe tailings are dominated by pyrrhotite. Hydrochemical models are established with computer codes for water-balance, sulphide oxidation rate and hydrochemical equilibrium calculations. The data input is based on detailed mineralogical, chemical and kinetic investigations carried out on the core of boreholes drilled in 2000 and 2003. The oxidation of pyrrhotite proceeds at a much faster rate than the oxidation of pyrite. The PYROX code, which is used for kinetic calculations, can take these differences into account by applying different oxide-coating diffusion coefficients (D2) for pyrrhotite and pyrite. Humidity-cell testing is widely used to predict the post-mining composition of drainage water in humid climates. However, the semiarid conditions at Matchless and Selebi-Phikwe only allow a minimal water flux within the dump. Under such conditions, humidity-cell testing is likely to overestimate the seepage-water pH. This is suggested by the hydrochemical equilibrium calculations for the post-mining period at Selebi-Phikwe, which predict a seepage-water pH about one unit lower than the pH at the end of the 26-weeks humidity-cell testing period. The acidity of the seepage water can be reduced by about half a pH unit, if an oxygen barrier below the evaporation zone is installed. A clay layer 0.5 m thick covered by >1.5 m tailings represents the optimal design for a wet barrier. All three computer codes used for water-balance calculations (HELP3, UNSAT-H and HYDRUS-1D), predict >85% average water saturation for such a layer, which diminishes the diffusion of oxygen into the pile and production of SO4−2 and H+. The alternative design for a dry barrier consists of a vegetated silt layer 1 m thick on top of the tailings. This barrier does not significantly influence the diffusion of oxygen although it reduces the net infiltration to ≤11 mm/year.

Long-term persistence of chromosome aberrations in uranium miners.

Chromosome aberration analyses were performed on blood samples from 165 active underground uranium miners between 1981 and 1985. After decommissioning the mine in 1997 chromosome aberration analyses were also included in the medical laboratory investigations of health conditions of 141 subjects between 1998 and 2002 within the framework of a follow-up-study. The numerical data are presented as functions of the exposure categories expressed in working level month up to 600. In the active groups the dicentric level was 7 to 12 times higher than in the unexposed population, the acentrics also higher with more than an order of magnitude, the frequency of total aberrations--including dicentrics, acentrics, rings, deletions, minits and numerical aberrations, i.e. both chromatid and chromosome type of aberrations were also well above the control level. In the group of former uranium miners although there were slight decreases in the dicentrics after 8 to 25 yr, the values were not significantly different from the values of active miners. The frequency of deletions was also maintained in the post-mining period. The frequency of acentrics, however, decreased significantly, but even the lowest values remained 2-3 times higher than the values in the unexposed population.The possibility is suggested that for the long-term persistence of cytogenetic alterations the permanent production and presence of clastogenic factors might be responsible. The comparison of the two datasets suggest a long-term persistence of cytogenetic alterations above the population average values in a large fraction of persons investigated.