| 1. |
- Corriols, Marvin, et al.
(författare)
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Geophysical characterization of the Leon-Chinandega aquifer, Nicaragua
- 2008
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 16:2, s. 349-362
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Tidskriftsartikel (refereegranskat)abstract
- Electrical geophysical surveys in the mode of vertical electrical soundings (VES) and continuous vertical electrical soundings (CVES) were conducted in the Leon-Chinandega plains, northwestern Nicaragua, in order to obtain detailed information about the geometry of the different hydrogeological layers in the aquifer and depth to the basement. A total of 51 VES were carried out within the plains. The results show a complex structure towards the north east of the area, and the southwestern part of the plains presents a smoother stratification. The geoelectrical measurements and borehole information indicate that the basement topography is characterized by hills and deep valleys with highly variable basement depths. Fifty CVES where done in a smaller area in the center of the plain. The resistivity data yielded considerable information revealing the existence of two main geo-electrical units. The combined interpretation of geological and geophysical data shows an environment typical of sedimentary volcanic coastal plains. The information collected during this investigation provides valuable data for estimating the fresh-water resources of the Leon-Chinandega aquifer system and for development of a groundwater management plan.
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| 2. |
- Danielsen, Jens E., et al.
(författare)
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Geophysical and hydrogeologic investigation of groundwater in the Karoo stratigraphic sequence at Sawmills in northern Matabeleland, Zimbabwe: a case history
- 2007
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 15:5, s. 945-960
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Tidskriftsartikel (refereegranskat)abstract
- Geophysical and hydrogeological investigations have been carried out around Sawmills in Zimbabwe, Africa. The investigations are components of a larger investigation to assess the groundwater potential of the Karoo sedimentary basin with regards to supplying water to Bulawayo City. The Sawmills area was selected due to the availability of borehole logs indicating favourable stratigraphy for groundwater availability and due to the high yields from the aquifers measured from these boreholes. Data collected using two geophysical methods are presented here: transient electromagnetic (TEM) and continuous vertical electrical sounding (CVES) data. The data have also been processed using laterally constrained inversion (LCI). Because the CVES provides greater detail in the shallow subsurface, whereas TEM is more effective at depth, a more accurate image of the entire subsurface profile is provided based on using both methods. The results suggest that LCI of CVES and TEM data, in the subsurface at the required depths at Sawmills, is able to provide a substantially more accurate image of the subsurface than either method alone. The hydrogeological interpretation of the geophysical data is valuable for determining the depth to and thickness of the potential aquifer horizon(s) and for identifying the position of potential recharge zones.
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| 3. |
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| 4. |
- Hasan, Md. Aziz, 1960-, et al.
(författare)
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Arsenic in shallow groundwater of Bangladesh : investigations from three different physiographic settings
- 2007
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 15:8, s. 1507-1522
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Tidskriftsartikel (refereegranskat)abstract
- Occurrences of arsenic (As) in the Bengal Basin of Bangladesh show close relationships with depositional environments and sediment textures. Hydrochemical data from three sites with varying physiography and sedimentation history show marked variations in redox status and dissolved As concentrations. Arsenic concentration in groundwater of the Ganges Flood Plain (GFP) is characteristically low, where high Mn concentrations indicate redox buffering by reduction of Mn(IV)-oxyhydroxides. Low DOC, HCO3-, NH4+ and high NO3- and So(4)(2-) concentrations reflect an elevated redox status in GFP aquifers. In contrast, As concentration in the Ganges Delta Plain (GDP) is very high along with high Fe and low Mn. In the Meghna Flood Plain (MFP), moderate to high As and Fe concentrations and low Mn are detected. Degradation of organic matter probably drives redox reactions in the aquifers, particularly in MFP and GDP, thereby mobilising dissolved As. Speciation calculations indicate supersaturation with respect to siderite and vivianite in the groundwater samples at MFP and GDP, but groundwater in the GFP wells is generally supersaturated with respect to rhodochrosite. Values of log P-CO2 at MFP and GDP sites are generally higher than at the GFP site. This is consistent with Mn(IV)-redox buffering suggested at the GFP site compared to Fe(III)-redox buffering at MFP and GDP sites.
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| 5. |
- Mendoza, J. A., et al.
(författare)
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Hydrogeological and hydrochemical features of an area polluted by heavy metals in central Nicaragua
- 2006
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 14:5, s. 777-784
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Tidskriftsartikel (refereegranskat)abstract
- Geophysical and hydrochemical surveys were used to investigate the hydrogeological conditions in one of the Rio Sucio microbasins, in central Nicaragua. Zones of vertical structures (i.e. fractures and quartz veins) and weathering were mapped using Continuous Vertical Electrical Soundings (CVES), as such zones are of major importance for groundwater transport. Water from the springs was analysed to determine concentrations of major ions and heavy metals. Low ion concentrations and 180 analyses indicate that the springs occur close to their recharge areas and there is a relatively rapid groundwater circulation. Mercury (Hg) content in the springs was low, while comparatively high amounts of lead (Pb) were found. The results presented here demonstrate the important function of weathering and tectonics in the occurrence of groundwater systems in the basin. Hg and Pb found in the springs' water reveal the existence of an increase in pollution sources disseminating in the area. More than 100 years of using mercury in the gold-mining industry and releasing wastes into rivers has affected water quality and ecosystems. Further investigations are needed in this area to determine the groundwater vulnerability to this pollution as this resource may be needed in the future.
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| 6. |
- Moreno, Luis, et al.
(författare)
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Can we use tracer tests to obtain data for performance assessment of repositories for nuclear waste?
- 2009
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 17:5, s. 1067-1080
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Tidskriftsartikel (refereegranskat)abstract
- With regard to the long-term safety of repositories for spent nuclear fuel, tracer tests have commonly been used in site characterisation (SC) for finding information that can be later used for performance assessment (PA). The question arises as to whether data obtained in tracer tests performed over a time scale of weeks or months are relevant for PA calculations. As part of a study overseen by the A"spo Task Force, the mechanisms that determine the radionuclide residence time under SC and PA conditions are addressed, given that they influence the validity of data transference from SC to PA. The results show that radionuclide transport in SC and PA, although governed by the same retardation mechanisms, are dominated by different sub-processes. In a practical sense this means that the parameter values (typically fracture apertures and "in situ" apparent retention data) determined in tracer tests, performed as a part of the SC program, should not be used directly for making PA predictions. The emphasis in SC should focus more on the determination of other parameters of relevance at PA timescales. The PA-specific flow rate, flow connectivity, and flow-wetted surface to flow ratio are given here as examples.
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| 7. |
- Odén, Magnus, et al.
(författare)
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From well-test data to input to stochastic continuum models: effect of the variable support scale of the hydraulic data
- 2006
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 14:8, s. 1409-1422
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Tidskriftsartikel (refereegranskat)abstract
- The question of how well the true underlying hydraulic conductivity statistics of heterogeneous media are captured by well tests is addressed. The hydraulic conductivity value and the corresponding support volume associated with a theoretical well are correlated, causing a bias in the statistics derived from well-test analyses. Statistics derived from numerically simulated well tests are compared with the known underlying conductivity statistics and the results indicate an under-prediction by simulations at higher hydraulic conductivities. The deviation starts at about mean conductivity and can be as large as an order of magnitude, with the conductivity in the vicinity of the well defining the upper boundary. In other words, the conductivity value interpreted from the well test cannot be larger than the value that the well test first encounters. Consequently, for data in this simulation exercise, the standard deviation, if only determined for the upper range of the conductivity values, would be underestimated by a factor of 1.6-2. While this specific range is likely to depend on the scale and degree of the underlying heterogeneity as well as the duration of the test, the results should be indicative of a more general behaviour and are likely to occur in other heterogeneous data as well.
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| 8. |
- Owen, Richard, et al.
(författare)
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The relationship between regional stress field, fracture orientation and depth of weathering and implications for groundwater prospecting in crystalline rocks
- 2007
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 15:7, s. 1231-1238
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Tidskriftsartikel (refereegranskat)abstract
- In a uniform granite gneiss study area in central Zimbabwe, lineaments oriented parallel to the maximum regional compressive stress orientation exhibit the thickest regolith development, while lineaments oriented perpendicular to the maximum compressive stress show the shallowest development of weathered regolith. The principal fracture set orientations were mapped using aerial imagery. The regional stress field, estimated from global stress maps, was used to determine the stresses acting on each principal lineament orientation. Multi-electrode resistivity profiling was carried out across fractures with different orientations to determine their subsurface regolith conditions. The results indicate that the 360 and 060 degrees lineaments, which are sub-parallel to the principal compressive stress orientation (sigma(1)) exhibit maximum development of the regolith, while 130 degrees lineaments perpendicular to sigma(1) do not exhibit significant regolith development. Since regolith thickness has been positively correlated with groundwater resources, it is suggested that fractures with orientations sub-parallel to the principal compressive stress direction constitute favourable groundwater targets. Knowledge of the regional stress field and fracture set orientations can be used as an effective low cost tool for locating potentially higher yielding boreholes in crystalline rock terrains.
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| 9. |
- Solomon, Semere, et al.
(författare)
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Groundwater study using remote sensing and geographic information systems (GIS) in the central highlands of Eritrea
- 2006
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 14:5, s. 729-741
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Tidskriftsartikel (refereegranskat)abstract
- Remote sensing, evaluation of digital elevation models (DEM), geographic information systems (GIS) and fieldwork techniques were combined to study the ground-water conditions in Eritrea. Remote sensing data were interpreted to produce lithological and lineament maps. DEM was used for lineament and geomorphologic mapping. Field studies permitted the study of structures and correlated them with lineament interpretations. Hydrogeological setting of springs and wells were investigated in the field, from well logs and pumping test data. All thematic layers were integrated and analysed in a GIS. Results show that groundwater occurrence is controlled by lithology, structures and landforms. Highest yields occur in basaltic rocks and are due to primary and secondary porosities. High yielding wells and springs are often related to large lineaments, lineament intersections and corresponding structural features. In metamorphic and igneous intrusive rocks with rugged landforms, groundwater occurs mainly in drainage channels with valley fill deposits. Zones of very good groundwater potential are characteristic for basaltic layers overlying lateritized crystalline rocks, flat topography with dense lineaments and structurally controlled drainage channels with valley fill deposits. The overall results demonstrate that the use of remote sensing and GIS provide potentially powerful tools to study groundwater resources and design a suitable exploration plan.
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| 10. |
- Solomon, Semere, et al.
(författare)
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Groundwater study using remote sensing and geographic information systems (GIS) in the central highlands of Eritrea (vol 14, pg 729, 2006)
- 2006
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Ingår i: Hydrogeology Journal. - : SPRINGER. - 1431-2174 .- 1435-0157. ; 14:6, s. 1029-1041
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Tidskriftsartikel (refereegranskat)abstract
- Remote sensing, evaluation of digital elevation models (DEM), geographic information systems (GIS) and fieldwork techniques were combined to study the groundwater conditions in Eritrea. Remote sensing data were interpreted to produce lithological and lineament maps. DEM was used for lineament and geomorphologic mapping. Field studies permitted the study of structures and correlated them with lineament interpretations. Hydrogeological setting of springs and wells were investigated in the field, from well logs and pumping test data. All thematic layers were integrated and analysed in a GIS. Results show that groundwater occurrence is controlled by lithology, structures and landforms. Highest yields occur in basaltic rocks and are due to primary and secondary porosities. High yielding wells and springs are often related to large lineaments, lineament intersections and corresponding structural features. In metamorphic and igneous intrusive rocks with rugged landforms, groundwater occurs mainly in drainage channels with valley fill deposits. Zones of very good groundwater potential are characteristic for basaltic layers overlying lateritized crystalline rocks, flat topography with dense lineaments and structurally controlled drainage channels with valley fill deposits. The overall results demonstrate that the use of remote sensing and GIS provide potentially powerful tools to study groundwater resources and design a suitable exploration plan.
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