Acid Mine Drainage Flow Research Articles

Current State of the Gold Mining Waste from the Ores of the Ursk Deposit (Western Siberia, Russia)

The article presents the original results of the investigation of sulfide-bearing mine tailings dumps (Ursk, Western Siberia, Russia), the adjacent territory, and acid mine drainage flows. The novelty of this study is related to integration of geophysical and geochemical data. The geoelectrical structure of the dump and the drainage valley was determined using the electrical resistivity tomography (ERT) method. Magnetic anomalies above the surface of the site were identified using ground magnetic surveys. The orthophotomap and a digital elevation model were obtained on the basis of aerial photography from an unmanned aircraft. The model of thermal imaging allows us to identify a number of temperature anomalies in the upper part of the dump slope and filtration zone in the drainage valley, caused by exothermic reactions. The digital relief model was constructed comprising three zones: (1) oxidation, (2) leaching, and (3) mixing and dilution. The oxidation zone is marked by low electrical resistivity (1–10 Ω·m), low pH values of the drainage waters (pH 3.61), low values of the modulus of the magnetic induction vector, and heating by +5 °C compared to the solid dump material that is not actively exposed to water. The oxidative conditions and low pH values favor the dilution of the Fe2+ compounds in the drainage solutions, which also contain Cu (3000 μg/L), Pb (1200 μg/L), As (1300 μg/L), and Hg (34 μg/L). The zone of the primary geochemical barrier is formed within the first 400 m, where the major proportion of dissolved elements if deposited. The second iron–aluminum sorption geochemical barrier is formed at a distance of 1000 m at the mixing zone with the Ur River. The stable geochemistry of surface waters, formed due to the inflow of drainage waters into the Ur River and further into the reservoir, persists at a distance of up to 7.7 km from the dump.

Improved imaging efficiency of large mine waste rock piles with integrated electrical and electromagnetic geophysical techniques

Acid mine drainage (AMD) can emanate from mine waste rock piles (WRPs) for extended periods, resulting in severe environmental contamination. Since the generation and release of AMD is dependent on the volume and composition of acid-generating waste rock, effective characterization of WRPs is necessary for successful long-term AMD management. Conventional methods such as coring and test pits are invasive and only provide sparsely distributed point information in WRPs which are typically large and highly heterogeneous. Geoelectrical methods such as direct current (DC) resistivity, time-domain induced polarization (TDIP) and electromagnetics (EM) can provide non-invasive and continuous information of WRPs. However, due to the enormous scale of typical WRPs, improved strategies are needed for more efficient imaging. The objective of this study was to demonstrate the improved efficiency of integrated imaging techniques with rapid but low-resolution EM, and laborious but high-resolution DC and TDIP, to characterize the acid-generating regions of a coal mine WRP in Nova Scotia, Canada. EM was first employed to rapidly image the entire pile footprint and locate zones with high conductivity. Focused 3D DC and TDIP surveys were then performed over these zones, which were <10% of entire WRP, to better characterize the associated waste rock composition. DC and TDIP images indicate coincident and continuous areas of low resistivity (<15 Ohm·m) and high chargeability (>15 mV/V), which are indicative of generated AMD (leachate) and stored AMD (sulfides), respectively. This interpretation is validated by corresponding geological and geochemical measurements within the WRP. This study demonstrates the value of integrating complementary electrical and electromagnetic methods for more efficient characterization of large mine WRPs, with EM rapidly locating zones of interest, and simultaneous DC and TDIP imaging then discriminating between areas that generate AMD and areas that are affected by AMD flow paths.

Geochemical audit of a historical tailings storage facility in Japan: Acid mine drainage formation, zinc migration and mitigation strategies

Historical tailings storage facilities (TSFs) are either abandoned or sparsely rehabilitated promoting acid mine drainage (AMD) formation and heavy metal release. To sustainably manage these sites, a geochemical audit coupled with numerical simulation to predict AMD flow paths and heavy metal migration are valuable. In this study, a 40-year-old TSF in Hokkaido, Japan was investigated. Tailings in this historical TSF contain pyrite (FeS2) while its copper (Cu) and zinc (Zn) contents were 1400–6440 mg/kg and 2800–22,300 mg/kg, respectively. Copper and Zn were also easily released in leaching tests because they are partitioned with the exchangeable phase (29% of Zn; 15% of Cu) and oxidizable fraction (25% of Zn; 33% of Cu). Kinetic modeling results attributed AMD formation to the interactions of pyrite and soluble phases in the tailings with oxygenated groundwater, which is supported by the sequential extraction and leaching results. Calibrations of groundwater/AMD flow and solute transport in the 2D reactive transport model were successfully done using hydraulic heads measured on-site and leaching results, respectively. The model forecasted the quality of AMD to deteriorate with time and AMD formation to continue for 1000 years. It also predicted ~24% AMD flux reduction, including lower Zn release with time when recharge reduction interventions are implemented on-site.

Effects of Acid Mine Drainage on Diversity of Macroinvertebrates at Morris Creek Watershed

Coal mining has played an important role in the history of West Virginia’s economy, but it is also the cause of a major environmental issue called acid mine drainage (AMD). AMD is caused by heavy metals from abandoned mines running into waterways and soils. AMD is a concern because many of the areas affected by AMD flow into larger water sources that are used for drinking and recreation. This is a problem because individuals are unknowingly consuming greater amounts of heavy metals and this can cause kidney dysfunction, nervous system disorders, and vascular damage in humans. The purpose of our study was to determine if AMD affected the diversity and abundance of aquatic insects in the Morris Creek Watershed. Two locations were sampled, an AMD site and a limestone-treated site. Water samples and macroinvertebrates were collected at these locations. Species were identified in both areas, and we used DNA barcoding, to further identify the macroinvertebrates. Ultimately, the diversity and abundance of species was greater at the area treated with limestone. These results indicated that the AMD influences diversity and abundance of species. This is important because the diversity of the environment determines the health of the environment and because diversity boosts productivity. With the results of our study in mind, we propose further research be conducted to examine the best treatment options to combat AMD and to boost environmental diversity.

Optimal start-up conditions for the efficient treatment of acid mine drainage using sulfate-reducing bioreactors based on physicochemical and microbiome analyses

Typically, sulfate-reducing bioreactors used to treat acid mine drainage (AMD) undergo an initial incubation period of a few weeks to acclimatize sulfate-reducing bacteria (SRB), although necessity of this preincubation has rarely been evaluated. To reduce time and economic cost, we developed an SRB acclimatization method using the continuous flow of AMD into bioreactors fed with rice bran, and compared with the conventional acclimatization method. We found that the SRB sufficiently acclimatized without the preincubation phase. Furthermore, we examined the performance and SRB communities in bioreactors operated for >200 days under seven different conditions, in which the amount of rice bran added and hydraulic retention times (HRTs) were varied. A comparison of the various bioreactor conditions revealed that the lowest rice bran amount (50 g) and the shortest HRT (6 h) caused a deterioration in reactor performance after day 144 and 229, respectively. In both cases, relatively aerobic environments developed due to the lack of organic matter seemed to inhibit sulfate reduction. Of the conditions tested, operation of the bioreactors with 200 g of rice bran and an HRT of 12.5 h was the most effective in treating AMD, showing a sulfate reduction rate of 20.7–77.9% during days 54–242. Data and materials availabilityAll data needed to evaluate the conclusions of this study are presented in the paper and/or the appendix.

Effects of long-term discharge of acid mine drainage from abandoned coal mines on soil microorganisms: microbial community structure, interaction patterns, and metabolic functions

More than twenty abandoned coal mines in the Yudong River Basin of Guizhou Province have discharged acid mine drainage (AMD) for a long time. The revelation of microbial community composition, interaction patterns, and metabolic functions can contribute to abetter understanding ofsuch ecosystems, which in its turn can be helpfulin the development of strategies aiming atthe ecological remediation of AMD pollution. In this study, reference and contaminated soil samples were collected along the AMD flow path for high-throughput sequencing. Results showed that the long-term AMD pollution promoted the evolution of γ-Proteobacteria, and the acidophilic iron-oxidizing bacteria Ferrovum (relative abundance of 15.50%) and iron-reducing bacteria Metallibacterium (9.87%) belonging to this class became the dominant genera. Co-occurrence analysis revealed that the proportion of positive correlations among bacteria increased from 51.02 (reference soil) to 75.16% (contaminated soil), suggesting that acidic pollution promotes the formation of mutualistic interaction networks of microorganisms. Metabolic function prediction (Tax4Fun) revealed that AMD contamination enhanced microbial functions such as translation, repair, and biosynthesis of peptidoglycan and lipopolysaccharide, etc., which may be an adaptive mechanism for microbial survival in extremely acidic environment. In addition, acidic pollution promoted the high expression of nitrogen-fixing genes in soil, and the discovery of autotrophic nitrogen-fixing bacteria such as Ferrovum highlights the possibility of using this taxon for bioremediation of AMD pollution.

Crab shell amendments enhance the abundance and diversity of key microbial groups in sulfate-reducing columns treating acid mine drainage.

Substrate amendments composed of crab shell (CS) waste materials have been shown to significantly improve the longevity and performance of acid mine drainage (AMD) treatment systems containing spent mushroom compost (SMC), yet the development of key microbial populations within these systems has not been investigated. To better understand the effects of CS on microbial dynamics in these systems, clone libraries and real-time quantitative PCR (qPCR) were performed on materials from a laboratory-scale AMD treatment system containing SMC and 0 to 100% CS substrate after receiving a continuous flow of AMD for 148 days (428 pore volumes). The proportion of CS in the substrate positively correlated with the diversity of sulfate-reducing bacteria (SRB) and archaeal clones, but negatively correlated with fungal diversity. CS also impacted microbial community structure, as revealed in Unifrac significance and principal coordinate analysis tests. The column containing 100% CS substrate supported 7 different genera of SRB-the most ever observed in an AMD treatment system. Moreover, the copy numbers of functional genes representing fermenters, sulfate reducers, and chitin degraders increased with increasing proportions of CS. These observations agree well with the chemical performance data, further validating that by supporting more abundant key microbial groups, chitinous substrates may provide benefits for improving both the longevity and performance of AMD treatment systems, and may provide similar benefits for the treatment of other environmental contaminants that are amenable to anaerobic bioremediation.Key points• Crab shell improves the longevity and performance of acid mine drainage treatment.• The diversity of sulfate-reducing bacteria is enhanced with crab shell amendments.• Crab shell supports more abundant key microbial groups than spent mushroom compost.

Hydrogelogical characterization of a waste rock pile and bedrock affected by acid mine drainage from geophysical survey

Mining activities are known for the profound changes they cause in the environment, especially those related to environmental liabilities generated by these enterprises. One major concern of this sector relies on the acid mine drainage (AMD) process, which is formed by the exposure of sulfide minerals to oxidizing conditions. As a result, the production of low-pH saline waters favors the mobilization of heavy metals to the environment. In the last decades, the characterization and monitoring of contamination plumes have become more feasible due to the application of geophysical tools, more precisely the DC resistivity geophysical method. Thus, the aim of the present study is the application of electrical resistivity tomography to understand the hydrogeological dynamic of a waste rock pile in the Osamu Utsumi uranium mine, with the identification of preferred groundwater and AMD flow. The analysis of the 2D geophysical products allowed the differentiation of high salinity water accumulation zones (< 40 Ω m) in the interior of the pile. Likewise, the evaluation of the pseudo-3D model generated by the interpolation of 2D sections was crucial for the recognition of low resistivity zones within the bedrock, possibly controlled by fractures that work as recharge zones between the waste rock pile and the fractured aquifer. The identification of discharge and recharge zones related to the fractures system is a fundamental step for planning and actions to prevent water–sulfides interaction process, which is responsible for the generation of AMD, and also the installation of groundwater pumping systems.

Arsenic oxidation and immobilization in acid mine drainage in karst areas

High concentrations of arsenic (As) occur in acid mine drainage (AMD), while the mechanisms governing its distribution along the flow of AMD are not fully understood. In this study, As species distribution was surveyed along the flow of an AMD in Jiaole coal mine in a typical kast area, in which length of creek is about 1100 m. AMD from the discharging source contained 1754.2 μg/L As (1570.0 μg/L in As (III)) and 644.1 mg/L Fe (all in Fe (II)) at pH 3.45. Both As and Fe concentrations decreased drastically to trace levels along the flow in the creek. As(III) oxidation to As(V) and Fe(II) oxidation to Fe(III) were discovered in a short distance from the discharging source. Lab experiments were performed to unveil the mechanisms governing As and Fe species distribution. Biological mechanism governed As(III) and Fe(II) oxidation in the AMD phase without contact with solid matrix, while different mechanisms governed the oxidation in the presence of solid matrix at different stages of AMD flow. At the beginning of AMD discharge, its contact with the soil matrix in rich of carbonate minerals in the karst area facilitated Fe(II) oxidation by O2 due to pH rise, which generated reactive oxidants for As(III) oxidation and iron oxyhydroxides for As adsorption or co-precipitation. Along the AMD flow, bacteria in the underlying sediments profoundly accelerated the biological oxidation of As(III) and Fe(II) as well as the co-precipitation into the sediments. Findings of this study deepen the understanding of As transport and transformation along the AMD flow, particularly in karst areas.

Temporal and spatial hydrogeochemical evolution and lead isotopic composition of a contaminated stream of Taxco, Guerrero, Mexico

Discharge of Acid Mine Drainage (AMD) produced within flooded mines is a major environmental issue in most polymetallic mining sites severely impacting nearby natural resources and producing a serious menace to the ecosystem and humans. The identification of both natural and anthropological factors influencing the bioavailability of toxic elements is relevant in revealing their behavior but also in the design of strategies for mitigating adverse effects to the environment. For these purposes, we carried out a spatial and seasonal hydrogeochemical (total and soluble contents) and a lead isotopic study of the AMD of the Xochula stream in the mining region of Taxco, Guerrero, in southern Mexico. The AMD is produced by the periodic discharge from the flooded Guerrero mine to the Xochula stream and is characterized by low to moderate pH, high sulfate, and high total and soluble metal contents. The AMD shows significant spatial but smaller temporal variations. Flow of AMD through a culvert made of concrete produces the most important chemical changes recorded regardless of the time of year significantly decreasing the electrical conductance and the concentration of total and soluble potentially toxic elements. Distribution of metals and As between dissolved and particulate-bound species is pH-controlled. Due to the short interaction time between the AMD and bedrock and the formation of coatings, lithology plays a minor role in neutralization, whereas mixing of AMD with freshwater is only significant in the less acidic segment of the stream. Neutralization of AMD entails a significant decrease of the concentration of both total and soluble metals and As and chemical speciation indicates that oxides, carbonates and sulfates are the reactive phases. The Pb isotopic composition reveals that metals derive from the Taxco ore deposit and that AMD is influenced by rocks of the Morelos and Taxco Schist formations.

Impact of acid mine drainage chemistry and microbiology on the development of efficient Fe removal activities

Coal mine derived acid mine drainage (AMD) is formed when oxygenated water infiltrates mine voids and oxidizes FeS phases, generating acidic fluid rich in heavy metals, polluting thousands of miles of streams. Existing remediation options are cost-prohibitive and difficult to sustain. In some cases, AMD flows over previously pristine soil in thin sheets over terrestrial surface, enhancing AMD aeration and Fe(II) oxidizing activities, leading to oxidative Fe(II) precipitation from AMD, without any human intervention. Since robust Fe(II) biooxidation occurs in the mixture of intruding AMD and pristine soil, understanding the effects of chemically variant AMD can be exploited for effective Fe(II) removal. We hypothesized that chemistry and microbiology of AMD intruding pristine soil on surface would influence the development of Fe(II) oxidizing capabilities. Therefore, to investigate the response of pristine soil to the addition of AMD varying in chemical and microbial characteristics, we mixed soil with a near-neutral and moderately acidic AMD, in separate incubations. Incubations with near-neutral AMD developed microbial Fe(II) oxidation activities after 10 days. However, Fe(II) oxidation in moderately acidic AMD incubations was mostly abiotic. 16S rRNA gene sequences and metabolic functional prediction (Tax4Fun) analysis of near-neutral AMD and soil mixture indicated development of taxonomically different communities capable of activities similar to microorganisms in a mine void. In conclusion, results indicate that AMD chemistry and microbiology affects development of Fe(II) biooxidation. Therefore, understanding of the effect of AMD chemistry on the development of FeOB activities in soil can be exploited to design site-specific and sustainable solutions.

Study of Generation and Underground Flow of Acid Mine Drainage in Waste Rock Pile in an Uranium Mine Using Electrical Resistivity Tomography

Mineral exploration is often associated with the generation of environmental liabilities, whose potential damages might imperil local water quality. An example of these environmental impacts is the acid mine drainage—AMD, caused by sulfides oxidation and production of acid and saline effluents. The analysis of critical areas with generation and spread of contamination plumes becomes more feasible due to the possibility to obtain geophysical models of water systems, especially to identify regions with accumulation of reactive minerals and preferential water flows. The rock-waste pile named BF-04 fits in this context of contamination, and it was studied based on the Electrical Resistivity Tomography technique, inversion models and isosurface models, providing conditions to recognize sulfide zones (> 10.1 mV/V), whereas chaotic high salt content underground flows, along several depths, were identified by low resistivity zones (< 75.8 Ω m). The complex behavior of groundwater flow in this kind of artificial granular aquifer is caused by its granulometric and lithologic heterogeneities, and compacted material. In addition, the results reveled a substantial water infiltration from Consulta creek, however the most critic zones for AMD generation are located at shallow levels where the waste rock material is more exposed to atmospheric O2 and meteoric water infiltration. The bedrock was not associated with significant low resistivity anomalies, which means that its contribution to AMD generation was considered relatively less important. The results will contribute to the environmental remediation management and also to demonstrate the potential applicability of geophysical methods in mining wastes.

Dynamics of Mn removal in an acid mine drainage treatment system over 13 years after installation

Acid mine drainage (AMD) from abandoned and active mines continues to pose a serious threat to the environment. Metal-rich fluids may emerge from abandoned mine works for hundreds of years, so the long-term performance of treatment systems must be evaluated to minimize the environmental impacts of AMD. A two-step process consisting of an aerobic wetland and a limestone bed is being used to treat coal mine-derived AMD in the Huff Run watershed of eastern Ohio, USA, and has been in operation for over 13 years. In 2002, the water was acidic (3.66 pH). From 2004 to 2014, water entering the treatment system had a pH of ~ 5.7 that increased to 7.25 by the time it exited the limestone bed. Since 2004, the effluent Al, Mn, and Fe concentrations have been between 0.05 and 0.12 mg/L, 0.04 and 0.25 mg/L, and 0.05 and 0.34 mg/L, respectively, with the majority of Fe and Al removal occurring in the wetland along with partial Mn removal. Subsequently, further Mn removal occurs as AMD flows through a limestone bed that was inoculated with a consortium of Mn(II)-oxidizing bacteria at the time of construction. An evaluation of historical system performance and current conditions indicate that effective metal removal has been sustained for over 13 years. While Mn(II)-oxidizing bacteria were most abundant in the limestone bed, they were detected throughout the system, indicating that indigenous Mn(II)-oxidizing microorganisms may be contributing to Mn removal well after the inoculation of the system.

Soil Infiltration, Permeability, and Rock Fracturing Assessment to Establish Water Flow Patterns in a Mine with Acid Mine Drainage

The flow of acid mine drainage (AMD) and neutral water were assessed inside an underground mine using a volumetric capacity technique, while water infiltration through the ground was assessed by performing three double ring constant load infiltrometer tests. Measured infiltration velocities were slow to moderate, between 0.036 and 2.07 cm/h. Total rainwater infiltration for the sub-basin was 0.031 hm3/yr. Tests performed on representative rock cores of the stratigraphical column of the area indicated that the permeabilities of the altered schist was 4.73E−10 cm/s, the tuff was 1.47E−09, and the graphitic phyllite was 2.47E−06. A structural analysis was performed inside the mine to assess fractures and faults using the mine plans for three different levels. Three major discontinuity paths were identified. Since the ground and rock permeabilities were low, the large water volumes inside the mine were attributed to these fractures. The results of this study are being used to understand flow patterns in the mine and to optimally locate a water treatment system to control the AMD.

Production of Hydroxyl radicals from oxygenation of simulated AMD due to CaCO3-induced pH increase

Many karst areas are impacted by acid mine drainage (AMD) which is characterized by low pH, high concentrations of dissolved Fe(II) and toxic contaminants. During the flow of AMD in karst areas, the increase in pH facilitates the oxygenation of Fe(II). Whereas, the oxidizing capacity for Fe(II) oxygenation in AMD is poorly understood. In light of the recent finding that hydroxyl radicals (OH) can be produced from Fe(II) oxygenation, this study experimentally measured the cumulative concentrations of OH produced from oxygenation of simulated AMD (8.93 mM Fe2+, pH 3) in the presence of limestone (CaCO3). With the increase in CaCO3 dosages from 0.67 to 2.78 g/L, Fe(II) oxidation rate increased accordingly, but the maximum concentration of cumulative OH appeared at the CaCO3 dosage of 1.39 g/L, being 59.3 μM within 24 h. The production of OH was mainly attributed to the rise of AMD pH due to dissolution of limestone, rendering the appearance of adsorbed Fe(II) on the newly formed lepidocrocite and ferrihydrite and complexed Fe2+ by carbonate (i.e., siderite). Oxygenation of these Fe(II) species was accountable for the production of OH. An appropriate pH (i.e., 5–6) was required for the moderate rate of Fe(II) oxidation, corresponding to the maximum production of OH. The OH produced from AMD oxygenation can concurrently oxidize the contaminants of arsenic and p-aminobenzenesulfonamide. Findings from this study suggest that the oxidizing impact of OH on contaminants transformation as well as organic carbon mineralization should be concerned for the oxygenation of AMD in karst areas.

Algal diversity in flowing waters at an acidic mine drainage “barrens” in central Pennsylvania, USA

Microscopic investigations were undertaken to decipher the diversity in the lotic algal communities from acidic waters (pH2.4-3.2) flowing overland in sheets and channels at an acid mine drainage (AMD) barrens near Kylertown, PA, USA. Microscopic observations, supplemented with taxonomic keys, aided in identification of the dominant algae, and measurement of carbon from adjacent soils was undertaken. The unicellular protist Euglena sp. was most abundant in slower flowing waters (i.e., pool near point of emergence and surficial flow sheets), while Ulothrix sp. was most abundant in faster flowing water from the central stream channel. A diverse range of unicellular microalgae such as Chlorella, Cylindrocystis, Botryococcus, and Navicula and several filamentous forms identified as Microspora, Cladophora, and Binuclearia were also recorded. The observed high algal diversity may be related to the long duration of AMD flow at this site which has led to the development of adapted algal communities. The comparatively higher carbon content in soil materials adjacent to slower flowing water sampling locations provides evidence for the important role of algae as primary producers in this extreme environment.

Diversity of Dissimilatory Sulfite Reductase Genes ( dsrAB ) in a Salt Marsh Impacted by Long-Term Acid Mine Drainage

Sulfate-reducing bacteria (SRB) play a major role in the coupled biogeochemical cycling of sulfur and chalcophilic metal(loid)s. By implication, they can exert a strong influence on the speciation and mobility of multiple metal(loid) contaminants. In this study, we combined DsrAB gene sequencing and sulfur isotopic profiling to identify the phylogeny and distribution of SRB and to assess their metabolic activity in salt marsh sediments exposed to acid mine drainage (AMD) for over 100 years. Recovered dsrAB sequences from three sites sampled along an AMD flow path indicated the dominance of a single Desulfovibrio species. Other major sequence clades were related most closely to Desulfosarcina, Desulfococcus, Desulfobulbus, and Desulfosporosinus species. The presence of metal sulfides with low delta(34)S values relative to delta(34)S values of pore water sulfate showed that sediment SRB populations were actively reducing sulfate under ambient conditions (pH of approximately 2), although possibly within less acidic microenvironments. Interestingly, delta(34)S values for pore water sulfate were lower than those for sulfate delivered during tidal inundation of marsh sediments. 16S rRNA gene sequence data from sediments and sulfur isotope data confirmed that sulfur-oxidizing bacteria drove the reoxidation of biogenic sulfide coupled to oxygen or nitrate reduction over a timescale of hours. Collectively, these findings imply a highly dynamic microbially mediated cycling of sulfate and sulfide, and thus the speciation and mobility of chalcophilic contaminant metal(loid)s, in AMD-impacted marsh sediments.

PATHWAYS OF ACID MINE DRAINAGE TO CLEAR LAKE: IMPLICATIONS FOR MERCURY CYCLING

Pore fluids from Clear Lake sediments collected near the abandoned Sulphur Bank Mercury Mine have low pH (locally <4) and elevated sulfate (> or =197 mmol/L), aluminum (> or =52 mmol/L), and iron (> or =28 mmol/L) contents derived from oxidation of sulfide minerals at the mine site. Acid mine drainage (AMD) is entering Clear Lake by advective subsurface flow nearest the mine and by diffusion at greater distances. Oxygen and hydrogen isotope ratios, combined with pore fluid compositions, constrain the sources and pathways of contaminated fluids. Sediment cores taken nearest the mine have the highest concentrations of dissolved sulfate, aluminum, and iron, which are contributed by direct subsurface flow of AMD from sulfide-bearing waste rock. Sediment cores as far as 100 m west of the Clear Lake shoreline show the presence of AMD that originated in the acidic lake that occupies the abandoned Herman Pit at the mine site. High sulfate content in the AMD has the potential to promote the activity of sulfate-reducing bacteria in the organic-rich lake sediments, which leads to methylation of Hg+2, making it both more toxic and bioavailable. Quantitative depletion of pore water sulfate at depth and sulfur isotope values of diagenetic pyrite near 0 per thousand indicate that sulfate availability limits the extent of sulfate reduction in the lake sediments away from the mine. Profiles of pore water sulfate in the sediments near the mine show that excess sulfate is available to support the activity of sulfate-reducing bacteria near the mine site. Enriched isotope values of dissolved sulfate (as high as 17.1 per thousand) and highly depleted isotope values for diagenetic pyrite (as low as -22.6 per thousand) indicate active bacterial sulfate reduction in the AMD-contaminated sediments. Sulfate- and iron-rich acid mine drainage entering Clear Lake by shallow subsurface flow likely needs to be controlled in order to lower the environmental impacts of Hg in the Clear Lake ecosystem.

Tropical Soils–Acid Mine Drainage Interactions: Breakthrough Curves and Some Transport Parameters

The interactions between acid mine drainage (AMD) and three tropical clayey soils have been studied through hydraulic conductivity and batch sorption/dissolution testing. After 19–24 pore volumes of AMD flow through the soils, the measured final hydraulic conductivity ranged between 1.1× 10−11 and 3.3× 10−11 m∕s . The pH, electrical conductivity, and solute breakthrough curves obtained suggested the soils had low acid-buffering capacities. Also, several chemical species were released from the soils due to AMD attack of soil grains and mineral. The batch tests revealed high dissolution of species such as sodium, cobalt, and sulfate from the soils by AMD. The results also indicated dissolution of metals from soil constituents, desorption of chemical species, and transformation and dissolution of soil minerals due to AMD attack. The results of the study showed that, in general, the soils were not effective in attenuating contaminants present in the AMD. Thus, they may not be used alone to construct liners fo...

English

The duration of acid mine drainage (AMD) flowing out of underground mines is important in watershed restoration and abandoned mine land reclamation projects. Past studies report that AMD flows from underground mines for hundreds of years with little change, while others find that poor drainage quality only lasts 20 to 40 years. In northern West Virginia, 20 above-drainage underground mines with AMD discharges were located and sampled during 1968, 1980, 2000, and 2005. Water flow, pH, acidity, Fe, Al, and sulfate were measured at all sampling times. From earlier work, 33 out of 44 sites (77%) were found to improve in drainage quality between 1968 and 2000. The results of the 2005 water sampling period confirmed these earlier findings. Out of 20 sites in the present study, only nine sites gave sufficient flow for water samples to be taken again in 2005. Of these nine discharges sampled in 2005, two showed a 22% and 32% increase of acidity, while the other seven sites (78%) decreased in acidity between 64 to 93%. Further sampling will quantify acidity changes of the original 44 above-drainage underground mine sites and more water samples will be collected during all four seasons of the year, which will represent both wet and dry periods. In this way, quantification of the effects of flow on underground mine chemistry may be evaluated. ______________________ 1 Paper presented at the 7 th International Conference on Acid Rock Drainage (ICARD), March 26-30, 2006, St. Louis MO. R.I. Barnhisel (ed.) Published by the American Society of Mining and Reclamation (ASMR), 3134 Montavesta Road, Lexington, KY 40502 2 Division of Plant and Soil Sciences, West Virginia University, Morgantown, WV; email: jskousen@wvu.edu, 304-293-6256. 3 New Miles of Blue Stream, 117 Lancaster, Philipsburg, PA 22408 7 th International Conference on Acid Rock Drainage, 2006 pp 2044-2054 DOI: 10.21000/JASMR06022044