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Uugulu, S.; Wanke, H. |
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Title |
Estimation of groundwater recharge in savannah aquifers along a precipitation gradient using chloride mass balance method and environmental isotopes, Namibia |
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Journal Article |
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Year |
2020 |
Publication  |
Physics and Chemistry of the Earth, Parts A/B/C |
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116 |
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102844 |
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Chloride mass balance, Groundwater recharge, Isotopic values, Precipitation gradient |
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The quantification of groundwater resources is essential especially in water scarce countries like Namibia. The chloride mass balance (CMB) method and isotopic composition were used in determining groundwater recharge along a precipitation gradient at three sites, namely: Tsumeb (600 mm/a precipitation); Waterberg (450 mm/a precipitation) and Kuzikus/Ebenhaezer (240 mm/a precipitation). Groundwater and rainwater were collected from year 2016–2017. Rainwater was collected monthly while groundwater was collected before, during and after rainy seasons. Rainwater isotopic values for δ18O and δ2H range from −10.70 to 6.10‰ and from −72.7 to 42.1‰ respectively. Groundwater isotopic values for δ18O range from −9.84 to −5.35‰ for Tsumeb; from −10.85 to −8.60‰ for Waterberg and from −8.24 to −1.56‰ for Kuzikus/Ebenhaezer, while that for δ2H range from −65.6 to −46.7‰ for Tsumeb; −69.4 to −61.2‰ for Waterberg and −54.2 to −22.7‰ for Kuzikus/Ebenhaezer. Rainwater scatters along the GMWL. Rainwater collected in January, February and March are more depleted in heavy isotopes than those in November, December, April and May. Waterberg groundwater plots on the GMWL which indicates absence of evaporation. Tsumeb groundwater plots on/close to the GMWL with an exception of groundwater from the karst Lake Otjikoto which is showing evaporation. Groundwater from Kuzikus/Ebenhaezer shows an evaporation effect, probably evaporation occurs during infiltration since it is observed in all sampling seasons. All groundwater from three sites plot in the same area with rainwater depleted in stable isotopic values, which could indicates that recharge only take place during January, February and March. CMB method revealed that Waterberg has the highest recharge rate ranging between 39.1 mm/a and 51.1 mm/a (8.7% – 11.4% of annual precipitation), Tsumeb with rates ranging from 21.1 mm/a to 48.5 mm/a (3.5% – 8.1% of annual precipitation), and lastly Kuzikus/Ebenhaezer from 3.2 mm/a to 17.5 mm/a (1.4% – 7.3% of annual precipitation). High recharge rates in Waterberg could be related to fast infiltration and absence of evaporation as indicated by the isotopic ratios. Differences in recharge rates cannot only be attributed to the precipitation gradient but also to the evaporation rates and the presence of preferential flow paths. Recharge rates estimated for these three sites can be used in managing the savannah aquifers especially at Kuzikus/Ebenhaezer where evaporation effect is observed that one can consider rain harvesting. |
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THL @ christoph.kuells @ uugulu_estimation_2020 |
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99 |
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Alexander, A.C.; Ndambuki, J.M. |
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Title |
Impact of mine closure on groundwater resource: Experience from Westrand Basin-South Africa |
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Journal Article |
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2023 |
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Physics and Chemistry of the Earth, Parts A/B/C |
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131 |
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103432 |
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Acid mine drainage, Groundwater quality, Mine closure, Spatio-temporal variation, Westrand Basin |
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The mining sector is at the edge of expanding to cater for natural resources that are much needed for technological development and manufacturing. Mushrooming of mines will consequently increase the number of mines closure. Moreover, mines closure have adverse impact on the environment at large and specifically on water resources. This study analyses historical groundwater quality parameters in mine intensive basin of Westrand Basin (WRB) to understand the status of groundwater quality in relation to mining activities and mine closure. Geographic information system (GIS) was used to map the spatio-temporal variation of groundwater quality in the basin and groundwater quality index (GQI) to evaluate its status. The coefficient of variation (CV) was applied to understand the stability of groundwater quality after the mine closure. Results indicated unstable and altered trend with increasing levels of acidity and salts concentration around the mines vicinity following the mine closure. The resultant maps indicated a significant deterioration of groundwater quality around the WRB with concentrations decreasing downstream. Obtained average GQI for the study period of 1996–2015 suggested a moderate groundwater quality at a range of GQI = 64–73. The CV indicated varying water quality at CV \textgreater 30% suggesting presence of source of contamination. Observed groundwater quality trends in Westrand basin suggested that mines closure present potential threat on groundwater quality and thus, a need for a robust mine closure plan and implementation. |
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THL @ christoph.kuells @ alexander_impact_2023 |
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134 |
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Mathuthu, M.; Uushona, V.; Indongo, V. |
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Title |
Radiological safety of groundwater around a uranium mine in Namibia |
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Journal Article |
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2021 |
Publication |
Physics and Chemistry of the Earth, Parts A/B/C |
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122 |
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102915 |
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Groundwater, ICP-MS, Radiological hazard, Uranium mining |
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Uranium mining activities produce the main element used in nuclear energy production. However, it can also negatively affect the environment including groundwater by release of residues or effluent containing radioactive elements. The study investigated the concentration and radiological hazard of uranium in groundwater and seepage water from the tailings of a uranium mine in Namibia. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to assess the concentration of uranium in the groundwater and seepage water and the radiological hazards were determined. The radiological hazard indices Radium equivalent activity (Raeq), Absorbed dose (D), Annual Effective Dose equivalent (AEDE), External hazard index (Hex) and Internal hazard index (Hin) were determined and compared to limits recommended by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The calculated average value of D and Hin of groundwater is 108.11nGyh−1 and 1.26, respectively and are above the UNSCEAR values (55 nGyh−1 and 1). Further, the average values of Raeq, AEDE and Hex were below the recommended values. The isotopic ratio of uranium radionuclides in groundwater indicates that the uranium in the sampled groundwater is below 1 suggesting it is not natural uranium present but a possible contamination from the mine seepage. The radiological hazard parameters of the seepage water were above the recommended values and thus pose a radiation risk to human and environment. |
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1474-7065 |
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THL @ christoph.kuells @ mathuthu_radiological_2021 |
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160 |
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Schwiede, M.; Duijnisveld, W.H.M.; Böttcher, J. |
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Investigation of processes leading to nitrate enrichment in soils in the Kalahari Region, Botswana |
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2005 |
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Physics and Chemistry of the Earth, Parts A/B/C |
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30 |
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11 |
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712-716 |
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Nitrate, Arenosol soils, Semi-arid, Kalahari, Cattle, Chloride, Travel time |
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In Southern Africa elevated nitrate concentrations are observed in mostly uninhabited semi-arid areas. In the Kalahari of Botswana groundwater locally exhibits concentrations up to 600mg/l. It is assumed, that nitrate found in the groundwater originates mainly from nitrogen input and transformations in the soils. Our investigations in the Kalahari between Serowe and Orapa show that cattle raising is an important source for enhanced nitrate concentrations in the soils (Arenosols). But also in termite mounds very high nitrate stocks were found, and under natural vegetation (acacia trees and shrubs) nitrate concentrations were mostly unexpectedly high. This nitrate enrichment in the soils poses a serious threat to the groundwater quality. However, calculated soil water age distributions in the unsaturated zone clearly show that today’s nitrate pollution of the groundwater below the investigation area could originate from natural sources, but cannot be caused by the current land use for cattle raising. |
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1474-7065 |
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Integrated Water Resources Management (IWRM) and the Millennium Development Goals: Managing Water for Peace and Prosperity |
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THL @ christoph.kuells @ Schwiede2005712 |
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276 |
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Merembayev, T.; Yunussov, R.; Yedilkhan, A. |
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Title |
Machine Learning Algorithms for Stratigraphy Classification on Uranium Deposits |
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2019 |
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Procedia Computer Science |
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150 |
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46-52 |
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classification, geophysics logging data, machine learning, stratigraphy, uranium deposit |
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Machine learning today becomes more and more effective instrument to solve many particular problems, where there are difficulties to apply well known and described math model. In other words – it is a great tool to describe non-linear phenomena. We tried to use this technique to improve existing process of stratigraphy, and reduce costs on site by applying computer leaded predictions on the basis of existing on-field collected data. Article describes usage of machine learning algorithms for stratigraphy boundaries classification based on geophysics logging data for uranium deposit in Kazakhstan. Correct marking of stratigraphy from geophysics logging data is complex non-linear task. To solve this task we applied several algorithms of machine learning: random forest, logistic regression, gradient boosting, k nearest neighbour and XGBoost. |
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1877-0509 |
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THL @ christoph.kuells @ merembayev_machine_2019 |
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113 |
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Love, A.J.; Shand, P.; Karlstrom, K.; Crossey, L.; Rousseau-Gueutin, P.; Priestley, S.; Wholing, D.; Fulton, S.; Keppel, M. |
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Geochemistry and Travertine Dating Provide New Insights into the Hydrogeology of the Great Artesian Basin, South Australia |
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Journal Article |
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2013 |
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Procedia Earth and Planetary Science |
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7 |
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521-524 |
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GAB springs, Great Artesian Basin, Helium isotope data, Uranium series dating |
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While of great national and societal significance, and importance in its own right, the Great Artesian Basin of Australia is an iconic example of a continental scale artesian groundwater system. New geochemical, hydrological, and neo-tectonic data suggests that existing models that involve recharge in eastern Australia, relatively simple flowpaths and discharge in springs in the western margin require modification. New geochemical data indicate a small volume flux of deeply derived (endogenic) fluids mixing into the aquifer system at a continental scale. Neo- tectonic data indicates active tectonism today that provides a fluid pathway through faults for the deeply sourced endogenic fluids to discharge in GAB travertine depositing springs. |
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1878-5220 |
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THL @ christoph.kuells @ love_geochemistry_2013 |
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122 |
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Lach, P.; Cathelineau, M.; Brouand, M.; Fiet, N. |
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In-situ Isotopic and Chemical Study of Pyrite from Chu-Sarysu (Kazakhstan) Roll-front Uranium Deposit |
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2015 |
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Procedia Earth and Planetary Science |
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13 |
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207-210 |
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LA-ICP-MS, pyrite, roll-front, SIMS, sulfur isotopy, traces elements, uranium |
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Pyrite is common in roll-front type uranium deposit in Chu-sarysu basin, Kazakhstan. Combined in-situ microstructural, isotopic and chemical analysis of pyrite indicates variation in precipitation conditions and in fluid composition. Broad-scale δ34S heterogeneity indicates a complex multi-facet evolution. First generation authigenic framboïdal aggregates are biogenic as demonstrated by the lowest δ34S values of -48‰ to -28‰. The latest generation pyrites are probably hydrothermal with greater δ34S variation (-30‰ to +12‰). This hydrothermal pyrite commonly displays variable enrichment of several trace elements especially As, Co and Ni. Strong variation in δ34S values and variable trace element enrichment is interpreted in terms of continuous variations in fluid composition. |
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1878-5220 |
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THL @ christoph.kuells @ lach_-situ_2015 |
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182 |
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Hu, K.; Wang, Q.; Tao, G.; Wang, A.; Ding, D. |
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Experimental Study on Restoration of Polluted Groundwater from in Situ Leaching Uranium Mining with Sulfate Reducing Bacteria and ZVI-SRB |
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2011 |
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Procedia Earth and Planetary Science |
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2 |
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150-155 |
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In situ leaching of uranium, nitrate radical, sulfate radical, Sulfate-Reducing Bacteria (SRB), Zero Valent Iron (ZVI) |
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In the case of in situ leaching of uranium, the primitive geochemical environment for groundwater is changed since leachant is injected into the water beaving uranium deposit. This increases the concentration of uranium and results in the groundwater contamination.Microbial reduction technology by Sulfate reducing bacteria and Zero Valent Iron were employed to treat uranium wastewater. The experiments were conducted to evaluate the influence of anion (sulfate and nitrate) on dealing with uranium wastewater. Experimental results show that the utilization of both SRB system and ZVI – SRB system to process uranium wastewater is affected by sulfate ion and nitrate ion. As the concentration of sulfate radical is lower than 4000mg/L, sulfate-reducing bacteria has no influence on precipitated uranium. However, as the concentration of sulfate is more than 6,000mg/L, uranium removal rate decreases significantly, from 80% to 14.1%. When adding sulfate radical on ZVI – SRB system to process uranium wastewater, its uranium removal rate is higher than SRB system. Low concentration of nitrate contributes to reduction metabolism of SRB. High concentration of nitrate inhibits the growth and metabolism of SRB and affects the treatment efficiency of uranium wastewater. When the concentration of nitrate reaches 1500mg/L, uranium removal rate is less than 0.1%. Nevertheless, as the concentration of nitrate is lower than 1000mg/L, uranium removal rate could reach more than 75%. As existence of nitrate radical, uranium removal rate of SRB by adding ZVI is higher than that without adding. |
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THL @ christoph.kuells @ hu_experimental_2011 |
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202 |
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Brook, G.A.; Marais, E.; Srivastava, P.; Jordan, T. |
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Timing of lake-level changes in Etosha Pan, Namibia, since the middle Holocene from OSL ages of relict shorelines in the Okondeka region |
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2007 |
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Quaternary International |
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175 |
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1 |
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29-40 |
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In 2003 examination of aerial photographs revealed a series of previously unknown relict shorelines on the arcuate ridge, possibly a clay lunette dune, that marks the western boundary of Etosha Pan in Namibia. The shorelines are 120–600m wide and the most prominent extend for tens of km around the lunette dune. The shorelines were examined on the ground in 2004 and an attempt was made to date the three lowest levels at ca. 5, 2.5 and 1m above the present pan surface. The OSL ages obtained indicate higher and more prolonged lake conditions than today at ca. 6.4, 4.0 and 2.1ka with the youngest shoreline sediments resting on an ancient pan surface dating to ca. 13ka. The evidence indicates dry conditions in the pan at ca. 13ka, wetter conditions and higher lake levels in the middle Holocene followed by a decline in lake levels to the present. Periods of inundation were of sufficient duration to produce shorelines at the southwestern end of the pan due to the prevailing northeasterly winds that would have maximized wave action along this section of the pan margin. The Etosha findings, together with other regional paleoclimate data, suggest four periods of increased wetness in SW Africa during the Holocene at 7–5, 4.5–3.5, 2.5–1.7 and ca. 1.0ka. There is widespread evidence for the oldest of these periods suggesting that it was a prominent and widespread interval of wetness. Prior to ca. 8.0ka the climate may have been drier than today. |
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1040-6182 |
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THL @ christoph.kuells @ brook_timing_2007 |
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97 |
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Stone, A. |
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Recharge investigations above the Stampriet Aquifer in semi-arid Namibia using geochemical methods and environmental tracers; sand, salt and water |
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2012 |
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Quaternary International |
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279-280 |
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470-471 |
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THL @ christoph.kuells @ stone_recharge_2012 |
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108 |
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