| 1. |
- Gomez Lopez, Etzar
(författare)
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Altiplanic aquifer exploration by multidisciplinary methods : Addressing the basis of sustainable use of groundwater
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The sustainable use of groundwater relies on building up three stages: exploration, development and management. The exploration is crucial to understand the capabilities and limitations of aquifer units; e.g. volume of available water and potential yield, distinction of recharge and discharge zones, and the groundwater quality are developed in this stage. In the Altiplano, groundwater is probably the most important water resource to supply domestic consumption and irrigation, since surficial bodies have been affected by reductions linked to drought events. The city of Oruro, Bolivia, in the Central Altiplano, is supplied solely with groundwater from a porous aquifer that has been utilized for decades; however, its hydrogeological characteristics are not fully understood due to the scarcity of data and limited resources to conduct long-term research. In order to develop the exploration of the aquifer units to the north of Oruro, this thesis presents studies aiming to fill gaps in the knowledge about their hydrogeological characteristics. A multidisciplinary approach including analysis of isotopic data and geoelectrical surveys was applied in this thesis; results and interpretations are based on data from previous studies and from sampling and measurements conducted recently within this work. The study subjects in this thesis include groundwater flow patterns inferred through isotopic characteristics, deduction of some geological features (fault mapping and delineation of bedrock) from changes in resistivity and estimation of aquifer parameters relating hydraulic properties and resistivity. Data acquisition during this work consisted of sampling and analysing isotopic compositions in water from precipitation, rivers and wells. Likewise, resistivity was obtained from surveys using electrical resistivity tomography and transient electromagnetic methods.Two aquifers were identified in the study area: unconsolidated sediments storing freshwater, currently under exploitation, overlying fractured bedrock that holds hydrothermal flows characterised by high temperature and salinity. Groundwater in the aquifers comes mainly from precipitation on the mountains, forming rivers that infiltrate laterally into the top aquifers, the natural discharge could have been located outside the limits of the study area, to the southwest; however, the cone of depression created by the wellfield supplying Oruro captures a substantial part of this groundwater. Isotopic characteristics of water in precipitation and groundwater at different depths were analysed to infer four circulation systems: (1) a shallow one receiving minor vertical infiltration, (2) the main system circulating through the unconsolidated sediments, (3) a transitional system between sediments and bedrock and (4) the deepest one, circulating through the bedrock fractures.Resistivity models obtained from geoelectrical surveys were analysed to infer the depth of the contact between sediments and bedrock; in the selected study area, it varies from a couple of meters to ~200 m. The shape of the bedrock is interpreted as complex and irregular. Likewise, extensions of faults underneath the sediments were detected by tracking changes in resistivity; some of them seem to be connected to the hydrothermal sources in the region. Finally, an empirical relationship between hydraulic conductivity (from pumping test) and resistivity in the porous aquifer was used to estimate aquifer parameters (hydraulic conductivity and transmissivity) in areas with available resistivity data.The outcomes from this thesis help to improve the basic comprehension of the hydrogeological characteristics of the studied aquifer system and fill gaps in the exploration stage; the results can be incorporated into the technical analyses aiming for the sustainable use of groundwater in the Altiplano. The applied methods have proven to be adequate to the local conditions and the multidisciplinary approach used in this thesis, can serve as an example for other studies dealing with similar conditions and limitations. Extensive surveys covering bigger areas with the same methodology, presented un this thesis, would permit the completion of the exploration stage and would make possible to shift the focus to the development and management stages of the aquifer units.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- Mutafela, Richard Nasilele, et al.
(författare)
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Geophysical investigation of glass 'hotspots' in glass dumps as potential secondary raw material sources
- 2020
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Ingår i: Waste Management. - : Elsevier. - 0956-053X .- 1879-2456. ; 106, s. 213-225
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the potential for Electrical Resistivity Tomography (ERT) to detect buried glass ‘hotspots’ in a glass waste dump based on results from an open glass dump investigated initially. This detection potential is vital for excavation and later use of buried materials as secondary resources. After ERT, test pits (TPs) were excavated around suspected glass hotspots and physico-chemical characterisation of the materials was done. Hotspots were successfully identified as regions of high resistivity (>8000 Ωm) and were thus confirmed by TPs which indicated mean glass composition of 87.2% among samples (up to 99% in some). However, high discrepancies in material resistivities increased the risk for introduction of artefacts, thus increasing the degree of uncertainty with depth, whereas similarities in resistivity between granite bedrock and crystal glass presented data misinterpretation risks. Nevertheless, suitable survey design, careful field procedures and caution exercised by basing data interpretations primarily on TP excavation observations generated good results particularly for near-surface materials, which is useful since glass waste dumps are inherently shallow. Thus, ERT could be a useful technique for obtaining more homogeneous excavated glass and other materials for use as secondary resources in metal extraction and other waste recycling techniques while eliminating complicated and often costly waste sorting needs.
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