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| 2. |
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| 3. |
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| 4. |
- Bhattacharya, Prosun, et al.
(författare)
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Hydrogeochemical study on the contamination of water resources in a part of Tarkwa mining area, Western Ghana
- 2012
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 1464-343X. ; 66-67, s. 72-84
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate the groundwater chemistry with special concern to metal pollution in selected communities in the Wassa West district, Ghana. In this mining area, 40 ground water samples, mainly from drilled wells, were collected. The groundwaters have generally from neutral to acidic pH values and their Eh values indicate oxidising conditions. The dominating ions are calcium, sodium, and bicarbonate. The metal concentrations in the study area are generally lower than those typically found in mining regions. Only 17 wells show metal concentrations exceeding WHO guidelines for at least one metal. The main contaminants are manganese and iron, but arsenic and aluminium also exceed the guidelines in some wells probably affected by acid mine drainage (AMD). Metal concentrations in the groundwater seem to be controlled by the adsorption processes. Hydrogeochemical modelling indicates supersaturation of groundwater with respect to several mineral phases including iron-hydroxides/oxides, suggesting that adsorption on these minerals may control heavy metal and arsenic concentrations in groundwater. The area is hilly, with many groundwater flow divides that result in several local flow systems. The aquifers therefore are not strongly affected by weathering of minerals due to short groundwater residence times and intense flushing. The local character of groundwater flow systems also prevents a strong impact of acid mine drainage on groundwater systems in a regional scale.
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| 5. |
- Earon, Robert
(författare)
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Water supply in hard rock coastal regions : The effect of heterogeneity and kinematic porosity
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water resources in hard rock terrain are difficult to characterize due to heterogeneity and anisotropy in the fracture network, low porosities and limited recharge volumes available during the summer season. Three methods were developed and evaluated in order to assist in water supply planning. A groundwater resources potential index was estimated using multivariate statistics, where physical and geological variables were classified using Analysis of Variance and Fisher's Least Significant Difference tests according to their effect on hydraulic properties. Principal component analysis was used to assign weights to the different classed variables. Classes and weights were used to produce an index referred to as groundwater resources potential (GRP), which correlated significantly with well data. Nearly 80% of the wells with less than median specific capacity values also had GRP values at those locations of zero or lower. Non-stationary variance was observed in specific capacity sub-samples taken from the Geological Survey of Sweden's well archive, despite homogeneous geology and topography. Spatial statistical analyses showed that spatial correlations were weak in well archive samples, implying that regional approximations based on sparse point data are highly error prone. Kinematic porosity estimated using superficial fracture measurements correlated significantly with well archive data. However, low correlation coefficients indicated that well data is likely not a suitable method for predicting water supply characteristics. This approach is an efficient method which shows promise in preliminary estimations of groundwater storage in heterogenic terrains. A groundwater balance model which describes seasonal groundwater storage changes was created in order to better approximate the groundwater situation often found in Swedish urbanized and semi-urbanized hard rock terrains. The model was based on a water budget approach at the pixel scale, and allows for approximation of well extraction which is not uniformly distributed in space. The model showed that in specific regions groundwater extraction may lead to severe decreases in groundwater level, where these impacts may not otherwise be expected. Dry season modelling with 10% increased evapotranspiration showed that in several areas groundwater reservoir depletion may be influenced by more than 50%.
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| 6. |
- Gómez, Etzar, et al.
(författare)
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Alluvial aquifer thickness and bedrock structure delineation by electromagnetic methods in the highlands of Bolivia
- 2019
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 78:3
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Tidskriftsartikel (refereegranskat)abstract
- The porous aquifers in the area called Challapampa are the most important groundwater reservoirs that supply drinking water to Oruro city in the highlands of Bolivia. They consist of unconsolidated fluvial–lacustrine deposits, resting on a complex sedimentary bedrock and covered by a thin surficial clay layer. The settings of these geological units and the structures governing the flow patterns have barely been investigated, despite this reservoir having been utilized during the last 50 years. This study applied transient electromagnetic (TEM) soundings and electrical resistivity tomography (ERT) in the middle part of the alluvial fan of River Paria to investigate the thickness of the porous aquifer and detect the relief of the bedrock. Likewise, some results expressed as resistivity models indicate the possible existence of geological structures below the unconsolidated sediments. The average depth of investigation reached in this study is between 200 and 250 m below the surface, for both the applied methods. The geological structures inferred have similar directions as the major faults in the vicinity, from southeast to northwest, which in turn are assumed as part of fractured aquifers underlying the porous aquifers. The geo-electrical techniques were successfully tested in the study area and the resistivity models from TEM complement very well those obtained from ERT. Therefore, extended investigations using the same techniques would help to develop a more complete description of the hydrogeological settings of the aquifer system.
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| 7. |
- Gómez, Etzar, et al.
(författare)
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Tracking of geological structures and detection of hydrothermal intrusion by geo-electrical methods in the highlands of Bolivia
- 2019
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Ingår i: Journal of South American Earth Sciences. - : Elsevier BV. - 0895-9811. ; 91, s. 214-226
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Tidskriftsartikel (refereegranskat)abstract
- Oruro city in the Bolivian highlands depends solely on groundwater to supply domestic consumption and irrigation. The top porous aquifer currently exploited is not fully understood in aspects like geometry, hydrogeological properties and interaction with other aquifers in the region. Recent studies detected traces of fractures in the bedrock beneath the porous aquifer; these geological structures seem to be part of a fractured aquifer in contact with thermal sources. The present study aims to fill the gap between those recently detected fractures and the well-mapped fault system to the east of the study area and identify hydrothermal flows by using geo-electrical methods like Electrical Resistivity Tomography and Transient Electromagnetic soundings. Thirteen tomographic lines, placed transversely to the direction of three main faults, were meant to identify prolongations of those structures by tracking distinctive low resistivity in sectors where saline water saturates the subsoil. This type of water is also present in some hot springs near Capachos, where hydrothermal flows discharge under artesian conditions. Two of the investigated faults seem extending to the northwest, in agreement with the expected linkage towards the recently detected fractures. These two faults appear to reach a volcanic formation since the hydrothermal flows, going mainly upwards, align with their strikes. The remaining fault seems not to be connected to any hydrothermal source. The study presents new information, data and interpretations intending to improve the knowledge about the geological structures in a sensitive part of the local aquifer system.
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| 8. |
- Gomez Lopez, Etzar, et al.
(författare)
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Groundwater Origins and Circulation Patterns Based on Isotopes in Challapampa Aquifer, Bolivia
- 2016
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 8:5
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Tidskriftsartikel (refereegranskat)abstract
- Aridity and seasonality of precipitation are characteristics of the highland region in Bolivia. Groundwater becomes an important and safe source of water when surficial bodies are intermittent and affected by natural and anthropogenic contamination. Decades of exploitation of the Challapampa aquifer, combined with lack of information required to understand the groundwater circulation, represent a challenge for reservoir management. This study analyzes isotopic compositions of deuterium and oxygen-18 in different stages in the hydrologic cycle to assess flow patterns in the aquifer, especially in the alluvial fan of River Paria, where records are more extensive in space and time. Interpretations are based on existing and new data. Some implications, such as the age of water, the evaporation effect in groundwater and some thermal intrusions are supported by stable isotopes, tritium, radiocarbon, and electrical conductivity records. New results confirm that modern precipitation over the mountains surrounding the study area is the most important origin of water for shallow aquifers until exploited depths, 100 m below surface. The origin of water in deeper depths, 400 m, seems related to infiltration at higher altitudes and longer residence times.
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| 9. |
- Gomez Lopez, Etzar, et al.
(författare)
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Quantitative estimations of aquifer properties from resistivity in the Bolivian highlands
- 2019
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Ingår i: H2Open Journal. - : IWA Publishing. - 2616-6518. ; 2:1, s. 113-124
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Tidskriftsartikel (refereegranskat)abstract
- Resistivity data constitute the largest part of the available information to assess the hydrogeological characteristics of the aquifer system near Oruro, in the central part of the Bolivian Altiplano. Two aquifers are part of this system; top unconsolidated sediments storing fresh water in their granular voids, overlying fractured hard rock formations where saline water was detected in connection to some faults. This study proposes an indirect and cost-effective way to estimate aquifer hydraulic properties for the groundwater management in the region. Hydraulic conductivity and transmissivity in the top aquifer were estimated using an empirical linear relationship between hydraulic conductivity and resistivity. This latter parameter, as well as the aquifer thickness, were obtained from the inverted models corresponding to the geoelectrical tests performed in the study area (electrical resistivity tomography, transient electromagnetic soundings and vertical electrical soundings). The highest estimated transmissivity values are ∼4.0 × 10−2 m2/s located in the centre of the study area, the lowest values are ∼3.4 × 10−3 m2/s, located around thermal intrusions to the south and where the top of the bedrock is shallow (∼20 m depth) to the west. The methodology presented in this study makes wider use of resistivity measurements to identify promising groundwater production sites.
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| 10. |
- Gonzales, Andres, et al.
(författare)
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A Multidisciplinary Approach for Clarifying the Recharge Processes and Origin of Saline Water in the Semi-Arid Punata Alluvial fan in Bolivia
- 2018
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- The analysis of stable isotopes assisted in identifying that groundwater in the Punata alluvial fan is mainly recharged by heavy flash floods, and the recharge from rainfall is of less importance. In addition, the hydrochemical analysis identified the Pucara River as the main source of recharge. Other streams in the north and northwest of the fan do not seem to contribute to the recharge. The hydrochemistry also shows that there is an increase of the Na+ and Cl− concentrations in the middle and distal part of the fan. The salinization of groundwater is most likely a result of the mixing of fresh water with residual saline pore water in the lacustrine deposits and/or ion exchange within these layers. Geophysical surveys assisted in describing the aquifer system layering, and indicated a fine-grained bottom layer where ion exchange might occur. This study demonstrates that the integration of several methods (e.g., hydrochemistry, hydrogeophysics, and stable isotopes) is valuable for clarifying ambiguities during the interpretation process and for characterizing hydrogeological processes in alluvial fans in general.
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| 11. |
- Gonzales, Andrés, et al.
(författare)
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Electrical resistivity tomography and induced polarization for mapping the subsurface of alluvial fans : A case study in Punata (Bolivia)
- 2016
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Ingår i: Geosciences (Switzerland). - : MDPI AG. - 2076-3263. ; 6:4
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Tidskriftsartikel (refereegranskat)abstract
- Conceptual models of aquifer systems can be refined and complemented with geophysical data, and they can assist in understanding hydrogeological properties such as groundwater storage capacity. This research attempts to use geoelectrical methods, Electrical Resistivity Tomography and Induced Polarization parameters, for mapping the subsurface in alluvial fans and to demonstrate its applicability; the Punata alluvial fan was used as a case study. The resistivity measurements proved to be a good tool for mapping the subsurface in the fan, especially when used in combination with Induced Polarization parameters (i.e., Normalized Chargeability). The Punata alluvial fan characterization indicated that the top part of the subsurface is composed of boulders in a matrix of finer particles and that the grain size decreases with depth; the electrical resistivity of these deposits ranged from 200 to 1000 Ωm, while the values of normalized chargeability were lower than 0.05 mS/m. The bottom of the aquifer system consisted of a layer with high clay content, and the resistivity ranged from 10 to 100 Ωm, while the normalized chargeability is higher than 0.07 mS/m. With the integration of these results and lithological information, a refined conceptual model is proposed; this model gives a more detailed description of the local aquifer system. It can be concluded that geoelectrical methods are useful for mapping aquifer systems in alluvial fans.
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| 12. |
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Grundvattendagarna 2013
- 2013
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Proceedings (redaktörskap) (refereegranskat)abstract
- Den här rapporten innehåller en sammanställning av abstracts som ligger till underlag för de presentationer som presenterades på konferensen Grundvattendagarna i Lund den 16–17 oktober 2013. Konferensen anordnades av SGU i samarbete med Geologiska institutionen på Lunds uni-versitet och Länsstyrelsen Skåne. Ett av konferensens syften var att få till en bred uppslutning från olika organisationer, myndigheter, konsulter, universitet, etc., och att skapa goda förutsättningar för att överföra kunskap och knyta kontakter för framtida samarbeten. Totalt har inte mindre än 59 olika bidrag kommit in och omfattningen på innehållet är verkligen stort. Det har varit en ära att få anordna konferensen och vi är tacksamma för det stora intresse som ni visat.
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| 13. |
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| 14. |
- Larsen, F, et al.
(författare)
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A preliminary analysis of the groundwater recharge to the Karoo formations, mid-Zambezi basin, Zimbabwe
- 2002
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Ingår i: Physics and Chemistry of the Earth. - 1474-7065. ; 27:11-22, s. 765-772
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Tidskriftsartikel (refereegranskat)abstract
- A multi-disciplinary study is being carried out on recharge to the Karoo sandstone aquifer in the western part of Zimbabwe, where recharge is controlled by the presence of a thick, confining basalt layer. The aquifer is geographically extensive, and has been identified throughout the southern part of the mid-Zambezi basin (Fig. 1). The potential for groundwater abstraction seems to be huge. The key issues in this part of the study are the extent of the recharge area and the recharge rates. The direct recharge area has previously been considered to be the area of outcrop of Karoo Forest sandstone, before it dips below an impervious basalt cover. However,, resistivity profiling shows that the basalt at the basin margin is weathered and fractured, and probably permeable, while the basalt deeper into the basin is fresh, solid and impermeable. Field and laboratory analysis of 22 groundwater samples support this extension of the recharge area to include a large area below the fractured basalt. CO2 gas pressures, calculated with the code PHREEQC using field measurements of pH and alkalinity, show that below the fractured basalt the groundwater is an open system in contact with atmospheric CO2. The C-14 and nitrate concentrations in this groundwater also indicate that recent infiltration takes place. The chloride contents of the rainfall and the groundwater in the recharge area have been measured to calculate direct recharge from rainfall. These data indicate that the direct recharge is in the range of 10-130 mm/yr, with an average value of 25 mm/yr. Preliminary results of recharge estimate using Cl-36 data suggests lower direct infiltration rates, but further studies are needed. The combination of hydro-chemical, isotopic and geophysical investigations show that the recharge area extends well beyond the sandstone outcrop area, northwards beneath the basalt some 20 km beyond the basalt margin.
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| 15. |
- Mendoza, Alfredo, et al.
(författare)
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Tidsserieanalys och grundvattenbildning längs Alnarpsdalen, Skåne.
- 2022
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Ingår i: ; , s. 1-1
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Konferensbidrag (refereegranskat)abstract
- Akvifären Alnarpsdalen är 6 - 10 km bred och sträcker sig från Skivarp i sydost till Löddeköpinge i nordväst och vidare ut i Öresund. Trots att flertalet kommuner i Skåne numera försörjs med vatten från Vombsjön eller Bolmen finns det kommuner, industrier och jordbrukare som använder vatten från Alnarpsdalen.Det finns ett antal frågor som kan ställas gällande Alnarpsdalen, till exempel hur mycket vatten som infiltreras eller hur stora uttag som kan göras, utan att riskera en ohållbar minskning av grundvattennivåer. Ett antal undersökningar har genomfört sedan 60-talet med syfte att svara på dessa frågor. Dessa undersökningar har gett viktig, men översiktlig information. För att få ökad förståelse finns behov av att genomföra mer detaljerade undersökningar.Med traditionella undersökningar beräknas hydrauliska parametrar genom provpumpningar. Denna metod fungerar bra, men är resurskrävande och resultaten gäller vanligtvis ett begränsat område. Användandet av tidsserieanalys kan vara en alternativ metod för att beräkna hydrauliska parametrar genom att observera naturliga grundvattennivåer. Tidsserieanalyser är ett relativt nytt forskningsområde inom hydrogeologi, vilket veterligen inte använts i södra Sverige. Trots att metoden under lång tid tillämpats inom t.ex. hydrologi, började användandet av tidsserieanalys inom hydrogeologi så sent som på 1990-talet. Detta projekts syfte var att studera sambanden mellan grundvattenbildning och grundvattennivåer längs Alnarpsdalen, vilket är ett av de viktigaste grundvattenmagasinen som finns i Skåne. Resultaten bidrar ny kunskap om cirkulationen under mark för vårt viktigaste livsmedel. Analysen utgår från användning av klassiska beräkningsmetoder anpassade till serier av grundvattennivåer, vilka har registrerats kontinuerligt i ett antal brunnar.Utgångsanalysen baserades på den så kallade Water-table fluctuation method, där variationer i grundvattennivåer med tid anses härröra från några faktorer. Dessa faktorer är nederbörd (infiltration), uttag, tidvatten, mm (Healy och Cook, 2002). Ett viktigt moment i analysen var att särskilja dessa olika faktorer i nivådata.Resultaten ger relevanta kunskaper om grundvattnet för framtida vattenförsörjningsplaner och skyddsåtgärder. Resultaten kan också vara viktiga för stadsplanering, eftersom kunskap om grundvattenbildning behövs för planering av ytor tillgängliga för urbanisering.
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| 16. |
- Picado, Francisco, et al.
(författare)
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Ecological, Groundwater, and Human Health Risk Assessment in a Mining Region of Nicaragua
- 2010
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Ingår i: Risk Analysis: an official publication of the Society for Risk Analysis. - : Wiley. - 1539-6924. ; 30:6, s. 916-933
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Tidskriftsartikel (refereegranskat)abstract
- Macroinvertebrates and fish in the contaminated river are faced with a higher risk to suffer from exposure to Hg than humans eating contaminated fish and bacteria living in the groundwater. The river sediment is the most hazardous source for the macroinvertebrates, and macroinvertebrates make up the highest risk for fish. The distribution of body concentrations of Hg in fish in the mining areas of the basin may exceed the distribution of endpoint values with close to 100% probability. Similarly, the Hg concentration in cord blood of humans feeding on fish from the river was predicted to exceed the BMDLs(0.1) with about 10% probability. Most of the risk to the groundwater quality is confined to the vicinity of the gold refining plants and along the river, with a probability of about 20% to exceed the guideline value.
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| 17. |
- Skeppström, Kirlna, 1976-
(författare)
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Radon in Groundwater- Influencing Factors and Prediction Methodology for a Swedish Environment
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a method for predicting radon (222Rn) levels in groundwater on a general scale, within an area of approximately 185 x 145 km2. The method applies to Swedish conditions, where 222Rn is the main contributor to natural radioactivity. Prediction of radon potential in groundwater is complex because there are many different factors affecting radon content, including geochemical and flow processes. The proposed method is based on univariate and multivariate statistical analyses and investigated the influence of different factors such as bedrock, soils, uranium distribution, altitude, distance to fractures and land use. A statistical variable based method (the RV method) was used to estimate risk values related to different radon concentrations. The method was calibrated and tested on more than 4400 drilled wells in Stockholm County. The weighted index (risk value) estimated by the RV method provided a fair prediction of radon potential in groundwater on a general scale. The RV method was successful in estimating the median radon concentration within 12 subregions (at a local scale, each of area 25 x 25 km2), based on weighted index values obtained from half of all wells tested. A high correlation between risk values and median radon concentrations was demonstrated. The factors bedrock, altitude, distance to fracture zone and distribution of uranium in bedrock were found to be significant in the prediction approach on a general scale. Visual data mining, which comprised analysis of 3D images, was a useful tool for data exploration but could not be used as an independent method for drawing conclusions regarding radon in groundwater. Results of a field study based on 38 drilled wells on the island of Ljusterö in the Stockholm archipelago showed that 222Rn concentrations in groundwater were weakly correlated to the parent elements (226Ra and 238U) in solution.
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