Redox zones are defined by steep gradients of changing concentrations and changing redox potential. They form a transition zone between oxic and anoxic/sulfidic conditions, where nitrate, manganese and iron reduction occurs. These redox zones can be situated in the sediment as well as in the water column. In the Baltic Sea both types are found. In the Bothnian Bay, the northernmost part of the Baltic Sea, the water column is well oxygenated and the redox zone lies within the uppermost sediment (approximately 2 cm in extend). In the Baltic Proper several of the deeper basins are stratified with the redox zone hanging between 75 and 100 m in the water column reaching up to 20 m.The redox-sensitive trace metal manganese can be both electron donor and acceptor in redox zones depending on its oxidation state. Manganese is transformed between the dissolved Mn(II),(III) and the particulate Mn(III/IV). Hence, Mn plays an important role in trace metal cycling across redox zones in natural environments. Manganese particles serve as a carrier for adsorbed trace metals towards the anoxic/sulfidic zone in the water column and as a barrier in the sediment, which restricts dissolved trace elements from diffusing to the oxic zone.In this study water samples (dissolved fraction, <0.22 μm, and particulate fraction, >0.22 μm) from the pelagic redox zone in Landsort Deep, Baltic proper were analyzed. Furthermore, a sedimentary redox zone from the Bothnian Bay has been investigated. A Mn particle peak is detected within the pelagic redox zone at Landsort Deep. A strong correlation between these Mn particles and several oxyanions as Mo, V and W is observed. The oxyanions are adsorbed onto the freshly formed Mn particles in the redox zone, settle with the particles and are released when Mn particles are reduced to Mn2+ and dissolve. This mechanism can act as a pump for trace metals to the sulfidic zone, where the trace metals either can be enriched in the dissolved fraction or form sulfid particles.In the sediment Mn redox cycling leads to enrichment of trace metals in the top layer. The formation of a barrier of Mn-Fe hydroxides restricts trace metal exchange between bottom water and sediment. Freshening of the Bothnian Bay basin has led to an increased sequestering of trace metals in the uppermost sediment. Trace metal proxies show that primary production in the Bothnian Bay has decreased starting approximately 2500 years BP. That led to a shift in the deposition of sulfide forming elements mainly due to the lower input of reactive organic carbon from plankton and to the recent enrichment of elements together with Mn-Fe hydroxides.

The geochemistry of iron (Fe) during freshwater transport and estuarine mixing has been investigated. Espescially the changes in the Fe-isotope signature have been studied. The fate of Fe-isotopes during estuarine mixing has been poorly studied. Sampling was performed in Kalix River, Kalix and Råne estuary, and in the open Bothnian Bay, Northern Baltic Sea. Water samples were filtered with 0.22 μm membrane filters. Both particulate (> 0.22 μm) and colloidal fractions (< 0.22 μm) were analyzed. Iron particles and colloids, with a negative Fe-isotope signature, are formed during spring flood in forested catchments. These Fe complexes are associated with organic carbon (OC), and probably have a mixed oxidation state (Fe(II,III)-OC). Negative colloids are labile and flocculate and/or oxidize during riverine transport. Therefore, no negative colloids are detectable in the estuaries of the open Bothnian Bay. Within the estuaries two types of ˜56Fe signatures were measured: negative particles and positive colloids. The open Bothnian Bay shows a third distinct group of positive particles. This group mirrors the rapid removal of Fe colloids and particles at low salinities. Most of the Fe has been removed from surface water at salinities below 1.0 psu. Data in this study show that the Fe-isotopes can be used to trace the origin and cycling of iron particles and colloids in the boreal landscape.

Prior to the remediation of brownfields, extensive sampling and analysing isdone. The planned and reached measurement uncertainties are seldom asked forcontracting such types of investigations. Therefore they are usually not statednor discussed in the tenders. Requirement for the performance of qualitycontrols generatingusable uncertainty estimates are seldom and no usefuluncertainty levels are either assumed. Such lack ofrequirements means that theuncertainty levels, of theresults used to draw conclusions, are often unknownmaking those conclusions uncertain. A further consequence is the absence ofverification if the used sampling and analytical strategies were appropriate, or ifother approaches should be used in future investigations.The aim of this thesis was to identify the relevant uncertainties in theinvestigation of contaminated soil, showhow they can be assessed by samplingand statistical evaluationsand how appropriate measurement uncertainty can beobtained by choosing analytical as well as sampling strategies.The study concluded that at a minimum, the measurement uncertainty in anenvironmental investigation should be properly estimated with all significantuncertainties listed and assessed, and kept as low aspossible based on availableresources.With forthcoming demands of certified samplers, the quality controls isexpected to increase and thereby theknowledge of uncertainty sources. Goodpractice and the needs for improvement will be identified. Quality controlsampling and statistical methods are available to assess the more commonsources of uncertainty, andsampling and analyticalmethods are applicable toreduce their effect.Increasing the use of more dynamic sampling strategies and analytical methods,the meas / I samband med sanering av förorenade områden utförs miljötekniskaundersökningar som innebär provtagning och analys av jordprover. Planerad ochfaktisk mätosäkerhet i dessa resultat brukar inte efterfrågas i förfrågnings-underlag för svenska miljötekniska undersökningar. Därav följer det naturligt attdessa uppgifter inte brukar specificeras i offerter och att det sällan sker någonkvalitetskontroll av utförda provtagningar som resulterar i en användbarosäkerhetsuppskattning. Det brukar ej heller antas och rapporteras någonanvändbar osäkerhetsnivå. Detta medför att osäkerheten i de resultat somanvänds för att dra slutsatser ofta är okänd vilket leder till osäkra slutsatser.Därför blir det inte heller klarlagt om använda provtagnings- och analys-strategier varit lämpliga eller om ett annat upplägg bör användas vid framtidaundersökningar. Syftet med denna avhandling är att visa vilka osäkerheter som finns i samband med undersökning av förorenade områden, hur de kan uppskattas med hjälp av provtagning och statistiska beräkningar samt hur lämplig mätosäkerhet kan erhållas genom val av provtagnings- och analysstrategi. Slutsatsen är, att som ett minimum bör en miljöteknisk undersöknings mätosäkerhet vara väl uppskattad, med alla viktiga osäkerheter inkluderade eller listade och värderade samt så liten som möjligt utifrån nedlagda resurser. Med kommande krav på certifierad provtagning lär medvetandet om källor till osäkerhet öka när osäkerheterna börjar kontrolleras och utvärderas. Det kommer att framgå vad som fungerar bra och vad som behöver förbättras. Kontroll-provstyper finns för att utvärdera de vanligaste källorna för mätosäkerhet och metoder finns för att minska deras inverkan. Genom att använda en mer dynamisk provtagningsstrategi med smartare användandeav befintliga analysmetoder kan mätosäkerheten minskas genom förtätad provtagning och bättre analyser.

Snowpack properties derived from hydrological models play an important role for many ecological, water resource, and climate applications; such as winter survival of plants, reindeer, small mammals and birds, avalanche hazards, glaciers and polar ice accumulation, growth of sea and lake ices, climate change, snow melt flooding etc. These hydrological models need accurate precipitation phase discrimination schemes to closely portray e. g. energy balance for melt and refreeze cycles, water lost to sublimation, and snow water equivalent within a watershed for the above applications. Precipitation phase is seldom reported from automated surface meteorological stations, so most hydrological models apply an empirical formula based on surface air temperature. There are many different empirical formulas used for precipitation type determination in hydrological models. The most commonly used formulas have one or two fixed air temperatures to separate rain from snow, however, some use more elaborate algorithms. The first part of this study consists of a comparison of common precipitation phase determination schemes to a database of 45 years of three-hour man-made weather observations for nineteen Swedish meteorological stations. These observations consist of surface air and dew point temperatures, precipitation mass and phase (classified as snow, rain, or mixed precipitation). Model schemes using two air temperature thresholds, one threshold all snow (TS) and one all rain (TR) having a linear snow fraction decrease between the thresholds (TS = 0.0˚C; TR = 2.0˚C, or TS = -1.0; TR = 3.0˚C) performed better than using a single rain/snow temperature threshold at all but two of 19 stations. A fitted air temperature dependent snow probability polynomial scheme resulted in similar, but slightly improved classification than a linear decreasing snow fraction approach at 13 of 19 locations. However, using the same empirical formula for all surface weather observations is a flawed technique since surface precipitation phase results from energy exchanges between falling precipitation and air in the lower atmosphere. Different lower atmospheric conditions cause dissimilar precipitation phase probabilities for near-freezing temperatures. Directly measured lower atmospheric conditions are seldom available for remote areas. However, meteorological observations occurring before/after similar air mass boundaries can be assumed to have alike atmospheric conditions which vary from most other observations. Therefore, hydrological models can indirectly account for lower atmospheric conditions. The second part of this study used twenty years of manual observations from eight U.S. weather stations to compare misclassified precipitation proportions when analyzing (a) all precipitation observations together and (b) identified cold air mass boundary observations (CAB) and non-CAB observations separately. The CAB observations were identified by a rapid surface air temperature decrease. Applying a linear decrease in snow fraction method, CAB had a TS (0˚C), and TR (4˚C) 1˚C warmer than non-CAB (-1˚C, 3˚C). Analyzing CAB and non-CAB separately reduced misclassified precipitation by 23%, from 7.0 to 5.4%.

Since the toxicity and mobility of trace metals are related to the metals' speciation, robust methods for trace metal speciation analysis are of great interest. During the last 15 years, hundreds of scientific articles have been published on the development and applications of the diffusive gradients in thin films (DGT) passive sampling technique.In this work the commercially available DGT containing ferrihydrite adsorbent, used for determination of phosphate and inorganic arsenic, was characterised with respect to anionic molybdate, antimonate, vanadate and tungstate determination. Tests were performed in the laboratory as well as in the field. Diffusion coefficients were determined for the anions using two different methods with good agreement. Simultaneous measurements of arsenate were conducted as quality control to facilitate comparison of the performance with previous work. The ferrihydrite-backed DGT was concluded useful for application over the pH-range 4 to 10 for vanadate and tungstate, and 4 to <8 for molybdate and antimonate. At pH values ≥8, deteriorating adsorption was observed.The combination of a restricted pore (RP) version of DGT and the normal open pore (OP) DGT was used for speciation of copper and nickel at three brackish water stations with different salinities in the Baltic Sea. Time series and depth profiles were taken, and complementary membrane- (<0.22 μm) and ultrafiltration (<1 kDa) was conducted. Comparing DGT and ultrafiltration measurements indicated that copper and nickel were complexed. Due to small differences in results between the OP and RP DGTs it was suggested that the complexes were smaller than the pore size of the RP gel (~1 nm) resulting in that both DGTs accumulating essentially the same fraction. Further, there seemed to be a trend in copper speciation indicating higher degree of strong complexation with increasing salinity. The low salinity stations are more affected by fluvial inputs which will likely affect the nature and composition of the organic ligands present. Assuming that copper forms more stable complexes with ligands of marine rather than terrestrial origin would be sufficient to explain the observed trend.

Process water discharged from mine sites may contain elevated concentrations of nitrogen (N) and phosphorus (P), which both are nutrients for algae and aquatic plants. Thus, discharge of nutrient rich mine water can result in algal blooms, eutrophication, oxygen deficiency and changed species composition in the receiving waters. This thesis is focused on the speciation and transformation processes of N and N:P ratios in streams and lakes receiving mine effluents from the Kiruna and Boliden mine sites. In this work, a dynamic biogeochemical model was developed for the clarification pond receiving ammonium-rich mine effluents from the Boliden concentration plant. A number of such models have been developed that simulate N transformations in wastewater stabilization ponds. However, few biogeochemical models have been developed that primarily focus on simulation of processes regulating transport and removal of N in waters receiving mine effluents. The presented model calculates concentrations of six N species and simulates the rate of 16 N transformation processes occurring in the water column and sediment as well as water-sediment and water-atmosphere interactions. A six-year simulation of ammonium concentrations showed stable behaviour over time, and the calibrated model rendered coefficients of determination (R2) of 0.93, 0.79 and 0.86 for the inorganic nitrogen species ammonium, nitrate and organic nitrogen, respectively. This indicates a stable model behaviour. The simulated denitrification rate was on average five times higher than the ammonia volatilization rate, and about three times higher than the permanent burial of sedimentary nitrogen. Hence, denitrification was the most important process for the permanent removal of N. The model can be used to simulate possible measures to reduce the N load and, after some modification and recalibration, it can be applied at other mine sites affected by N-rich effluents. In addition, it was investigated which nutrient that limits bioproduction in the two aquatic systems. Total nitrogen (TN), total phosphorus (TP) and N:P ratios in water, sediment and macrophytes were used to examine (1) spatial variations within the systems, (2) differences between the systems and (3) seasonal variations. The TN content from the discharge point at the Kiruna site was on average about seven times higher than at the Boliden discharge point, while the TP content was 10 times lower than in the discharge point at the Boliden site. Depending on the ammonium concentration in the effluent at the Boliden site, N:P-ratios of the water column shifted from being >22, indicating P-deficiency, to between 9-22, indicating a transition from N to P deficiency (co-limitation). However, water column N:P ratios at the Kiruna site always indicated P deficiency. On the other hand, the N:P ratios of macrophytes revealed that both sites may vary from N to P limitation. These differences are important to consider when establishing a monitoring programme for assessing the environmental influence of nutrient rich mine effluents. Such a programme should include the major N and P species of the water as well as samples of phytoplankton, sediment and macrophytes.

Many countries around the world use coal as fuel for the purpose of power generation. The extraction of coal produces large volumes of waste rock (WR) that are sometimes sulphide rich (principally containing iron sulphides such as pyrite (FeS2) and pyrrhotite (Fe1-xS)), with varying quantities of trace elements such as As, Si, Cu, Zn, Ni, Co, Mo and Cr etc). Such waste is environmentally sensitive due to the risk of oxidation in presence of atmospheric oxygen and water. Sulphide oxidation may result in acidic waters (acid mine drainage, AMD), which often contains high loads of dissolved metals. Coal combustion results in large amounts of fly ash (FA), which also is of environmental concern. However, FA is alkaline and may potentially be used for neutralisation of AMD. Therefore, the AMD producing potential of WR from coal mining and the neutralisation potential of FAs from coal and biomass combustion was studied with the ultimate goal to develop a methodology to decrease the environmental problems related to these materials.WR was sampled form the Lakhra coal field in Pakistan, which has an estimated coal reserve of 1.3 Bton, from lignite to sub-bituminous in quality. The WR samples were characterised by mineralogical and geochemical methods and the acid producing potential was determined by static (Acid Base Accounting) and kinetic (modified humidity cells test) methods. Besides organic material, the WRs are composed of quartz, pyrite, kaolinite, hematite and gypsum with varying amounts of calcite, lime, malladerite, spangolite, franklinite and birnessite. The Lakhra WR has strong potential to generate AMD (-70 to -492 kg CaCO3/ton) and pollute natural waters by leaching of elements such as Cd, Co, Cr, Cu, Ni, Pb, Zn, Fe and SO42-. Three different FAs based on the origin, fuel type and storage methods were studied. They were characterised by mineralogical and geochemical methods, the leachability was studied by batch leaching tests and the potential for buffering acids and neutralisation of AMD was quantified. Fly ash from burning i) brown coal (lignite) in Pakistan (PK), ii) black (bituminous) coal from Finland (FI) and iii) biomass FA provided by a sulphate pulp and paper mill in Sweden (SE) were studied. All ashes contained quarts, PK also iron oxide, anhydrite, and magnesioferrite, FI also mullite and lime, and SE also calcite and anorthite. All ashes were enriched in As, Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn compared to continental crust, and all ashes had a strong neutralisation potential, the bioash, SE, in particular. The results are encouraging and suggest that it is possible to use FA to mitigate the environmental problems with coal mine WR. Methods for that will be the focus for the continued research.

Waste rock and tailings generated by sulphide ore mining often contains large amounts of iron sulphides which oxidize when exposed to atmospheric oxygen and may generate acidity. In the absence of alkaline minerals to neutralize this acidity, elements including harmful heavy metals become mobile. Clearly, it is a high priority for mining operations to reduce the impact of mining waste on the environment. New research aimed to take advantage of industrial rest products to inhibit acid mine drainage has yielded some reason for optimism. The recycling of chemicals in sulphate pulp mills yields green liquor dregs (GLD). The fact that GLD have a low hydraulic conductivity and are alkaline opens the possibility of using it for construction of sealing layers for sulphidic mine waste. The study consists of two parts. The aim of the first part was to characterize the GLD and evaluate their suitability for sealing layer purposes. GLD were characterized physically, mineralogically and chemically to define variations in the properties of the material and to evaluate if they can act as a potential candidate for construction of sealing layers. Compared to lime, the pure GLD appear to have a higher porosity and surface area even though both materials have comparable particle size. The shear strength may, however, be insufficient. In cover applications, where high compaction grade and low hydraulic conductivity are desirable, mixing additives to GLD is necessary to improve the material properties. Based on the characterization results, the difference between batches is fairly small both mineralogically and physically. GLD could be an alternative to traditional sealing layers made of till since it was shown to have relatively low hydraulic conductivity and high water retention potential. The small particle size and high buffer capacity makes it a better candidate than till which usually varies in size and hydraulic conductivity. There is a chemical variation of the material but the element content does not seem to be an environmental concern.The aim of the second part of the study was to improve the performance of the GLD by blending them with other rest products. Geotechnical and geochemical investigations were performed on GLD mixed with tailings. Humidity cell tests were used to study the effect of GLD on the mobility of elements considered to be major environmental issues in the tailings. By adding tailings to GLD, the shear strength improved 2-3 times after 1 month of curing. The water retention capacity remained at a high level. Humidity cell tests revealed that a 50/50 mix of GLD and tailings has a direct effect on the metal leaching from tailings. The alkaline capacity of the pulping waste raised the pH, thereby stabilizing the tailings and reducing the leaching of Al, Cd, Cu, Ni, Co, Cr and Mn. The amount of leached elements could be directly related to the pH during the test. Elements that showed an increase of leaching as a result of the application of GLD were Mo and As. This is explained by the chemical behavior of these elements and their tendency to become mobile at high pH.In summary, GLD have the potential to both reduce the amount of leachate generated in tailings and, due to their alkaline property, improve the leachate quality by decreasing the metal mobility. However, restrictions occur when GLD are blended with tailings containing large amounts of As and Mo since an increased leaching may be expected. Further research will focus on the aging of the material and its long-term stability.

High precision isotope ratio measurements have found increasing application in various branches of science, from classical isotope geochronology to complex multi-tracer experiments in environmental studies. Progress in analytical technologies in recent years has allowed higher quality data to be obtained through mass spectrometry. Major pitfalls lie in challenges to obtain accurate and reliable isotopic data for trace and ultra-trace element by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Sources of errors must therefore be accurately evaluated and avoided at every procedural step. The present study has been focused on analytical method development, optimization and evaluation (including sample preparation, matrix separation, instrumental analysis and data evaluation stages) for isotopic and multi-elemental analyses in environmental samples at trace and ultra-trace levels. The first method tested and optimized has allowed obtaining both osmium concentration and isotopic ratio (187Os/188Os) data together with broad multi-elemental characterization of samples. The procedure was as follows: digestion of small biological samples spiked with Os (enriched in 190Os) followed by concentration and Os isotope measurements by ICP- SFMS, operated with solution nebulization (SN) introduction system and methane addition to the plasma. A specific gas-phase introduction (GPI) system was adopted for samples with low analyte content (&lt;500 pg) for isotopic measurements. Memory effects were avoided with implementation of disposable plastic lab ware. This resulted in a relatively inexpensive and rapid method with high sample throughput capability. SN method limit of detection (MLOD) did not improve compared to previous studies (2 pg g-1), while a MLOD of 0.2 pg g-1 obtained with GPI represents an important improvement, especially taking into account potential further gains due to refined digestion stage. Method reproducibility for 187Os/188Os evaluated using in-house control samples was better than 1.5% RSD. The method, successively applied to a large scale bio-monitoring case, confirmed the presence of an anthropogenic Os in animals from an area affected by emissions from a stainless steel foundry. The second method has been focused on Cd concentration and isotope ratio measurements. Different analytical stages were critically evaluated and optimized for processing carbon-rich environmental samples. Several digestion methods were tested (high pressure ashing, microwave, ultrawave and ashing) followed by ion-exchange chromatography to separate analyte from matrix. Concentrations were measured by ICP-SFMS and subsequently isotopic ratio measurements were performed using Neptune Plus MC-ICP-MS. The latter was tested with two different introduction configurations: a standard SN system and a high sensitivity setup (Aridus II desolvating nebulizer). Overall reproducibility of the method was assessed by replicate preparation and Cd isotope ratio measurements in various environmental matrices (soil, sediments, Fe-Mn nodules, sludge, kidney, liver, leaves, mushroom, lichen) and was found to be better than 0.1‰ (2σ for δ114Cd/110Cd) for the majority of samples. Purification performances were evaluated by analyzing the different elution fractions collected at each separation step by ICP-SFMS. Cadmium recovery in the purified fraction was above 95% for all samples analyzed. Spectrally interfering elements such as Mo and Sn might partially co-elute in the Cd fraction and their effect on isotope ratios was carefully investigated. Though the use of a desolvating nebulizer increases the instrumental sensitivity and reduces oxide formation, at the same time it resulted in degraded in-run precision because of poorer signal stability. Accuracy was difficult to assess due to the absence of certified Cd isotopic values. Therefore, Cd isotope data for several commercially-available reference materials are presented and compared with previously published results where available. The method was then applied to variety of biological samples including birch leaves (Betula pubescenes) collected from various locations and different seasons. Birch leaves showed fractionation towards heavier isotopes with a mean δ114Cd/110Cd of 0.7‰ and found to be influenced by seasonal variations. The reason for such fractionation is assumed to be derived from sample uptake through the root system and translocation in the plant. Cd isotopic patterns were compared with other isotopic systems (Zn, Os, Pb) to provide a more comprehensive view of the observed variations.

Successful mine waste reclamation is a fundamental aspect in mine plan development and is legislated through the European Parliament’s ‘Management of Waste from Extractive Industries Directive (2006/21/EC)’. Field and pilot-scale trials were utilised to evaluate different applications of an alternative cover material, sewage sludge, in its ability to remediate and prevent acid rock drainage formation from sulphidic mine tailings derived from the Kristineberg Zn-Cu mine, northern Sweden. Sewage sludge is an organically-rich waste material generated from the treatment of domestic waste water. It may function suitably as a low permeable barrier against oxygen ingress when compacted or as a surface vegetation substrate. The first study focused on evaluating the effectiveness of a sewage sludge sealing layer, part of a composite dry cover design system. Data on tailings, leachate water and pore gas geochemistry during eight years from two experimental pilot-scale test cells revealed that the sludge was an effective barrier to oxygen influx, which prevented sulphide oxidation and acid rock drainage formation. Sludge-borne metals (Cd, Co, Cu, Fe, Pb, Zn) precipitated and were retained in the underlying tailings due to the reduced conditions produced, resulting in low concentrations of dissolved metals (<10μg/L Cd, Co, Cu, Ni, Pb, Zn) in the drainage, several orders of magnitude lower than that from an uncovered tailings reference cell. However, a 19.6% mass reduction of the sludge due to organic matter degradation may compromise the effectiveness of the cover in the long-term. The second study evaluated the geochemical impact of a field-scale surface application of sewage sludge on the groundwater quality of a formally-remediated sulphidic-tailings impoundment. Thirteen years after initial remediation, 12 000 tonnes of sludge were applied to a depth of 0.3m to re-vegetate and stabilise the pre-existing water-saturated and composite dry cover design systems. After two years, a 17% reduction of the sludge volume occurred due largely to aerobic degradation of the organic matter fraction, leaching of the constituents Ca and S, and partially due to the leaching of Cu, Ni, Pb and Zn. Groundwater data indicated that sludge-borne constituents derived from the dry covered areas were prevented from infiltrating through the low permeable sealing layer. Instead they drained laterally through the protective layer to the impoundment toe and did not reach nor have a negative impact on the tailings groundwater. Oppositely, a major plume of sludge-borne constituents derived from the water-saturated area entered the tailings groundwater vertically unhindered, then dispersed laterally through the tailings due to the dominating hydrogeological regime. The plume migrated underneath the dry composite covered area after 2.2 years, where concentrations of Cu (188µg/L), Fe (254mg/L), Ni (263µg/L), Pb (95µg/L) and Zn (1.55mg/L) peaked. The plume included elevated nitrate concentrations (167mg/L) released from nitrification of ammonium in the sludge, which oxidised pyrite in the tailings. However, the effects were temporary due to declining sludge-borne nitrate and metal release from the sludge due to vegetation establishment after 2 years. The expected duration of the plume to disperse and exit the tailings impoundment is estimated to take another 4 years. In conclusion, these studies have found that sewage sludge can be effectively utilised as a suitable alternative cover material within the study periods observed as a sealing layer and as a final vegetation substrate on composite dry covers, but not water-saturated covered systems for the remediation of sulphidic mine tailings. Further investigations will have to verify the effectiveness of these applications in the long-term.