Water-bearing Zones Research Articles

Delineation of potential ground water-bearing zones in the Barind tract of West Bengal, India

The Barind tract of West Bengal is an area of tropical sub-humid region composed of old alluvial soil. The area has high water demand due to growing population pressure and intensification in agricultural activity. These create huge stress on surface and ground water availability. Continuous withdrawal of ground water has become an alternative source of irrigation water which has also again made the condition critical. Ground water level has been lowered down drastically in many parts in this region. Under this circumstance, it is necessary to delineate potential ground water-bearing layers. Therefore, the present study attempts to identify potential ground water-bearing zones to manage ground water effectively. Instead of usually used parameters for ground water potentiality delineation here only some particular litholog parameters like breadth of water-bearing layer, depth of water-bearing layer, presence of clay layer above or below major water-bearing layer have been considered for delimiting the same. The result shows that out of total area, 60% area (405,382.2 ha) falls under very low to low potential ground water-bearing zone and only 8.19% area (55,634.97 ha) is potential. Considering this spatial pattern of ground water availability, harvesting structure and magnitude of water withdrawing should be designed.

Pb-Sr isotopic and geochemical constraints on sources and processes of lead contamination in well waters and soil from former fruit orchards, Pennsylvania, USA: A legacy of anthropogenic activities

Isotopic discrimination can be an effective tool in establishing a direct link between sources of Pb contamination and the presence of anomalously high concentrations of Pb in waters, soils, and organisms. Residential wells supplying water containing up to 1600ppb Pb to houses built on the former Mohr orchards commercial site, near Allentown, PA, were evaluated to discern anthropogenic from geogenic sources. Pb (n=144) and Sr (n=40) isotopic data and REE (n=29) data were determined for waters from residential wells, test wells (drilled for this study), and surface waters from pond and creeks. Local soils, sediments, bedrock, Zn-Pb mineralization and coal were also analyzed (n=94), together with locally used Pb-As pesticide (n=5). Waters from residential and test wells show overlapping values of 206Pb/207Pb, 208Pb/207Pb and 87Sr/86Sr. Larger negative Ce anomalies (Ce/Ce*) distinguish residential wells from test wells. Results show that residential and test well waters, sediments from residential water filters in water tanks, and surface waters display broad linear trends in Pb isotope plots. Pb isotope data for soils, bedrock, and pesticides have contrasting ranges and overlapping trends. Contributions of Pb from soils to residential well waters are limited and implicated primarily in wells having shallow water-bearing zones and carrying high sediment contents. Pb isotope data for residential wells, test wells, and surface waters show substantial overlap with Pb data reflecting anthropogenic actions (e.g., burning fossil fuels, industrial and urban processing activities). Limited contributions of Pb from bedrock, soils, and pesticides are evident. High Pb concentrations in the residential waters are likely related to sediment build up in residential water tanks. Redox reactions, triggered by influx of groundwater via wells into the residential water systems and leading to subtle changes in pH, are implicated in precipitation of Fe oxyhydroxides, oxidative scavenging of Ce(IV), and desorption and release of Pb into the residential water systems. The Pb isotope features in the residences and the region are best interpreted as reflecting a legacy of industrial Pb present in underlying aquifers that currently supply the drinking water wells.

Post-glacial reactivation of the Bollnäs fault, central Sweden – a multidisciplinary geophysical investigation

Abstract. Glacially induced intraplate faults are conspicuous in Fennoscandia where they reach trace lengths of up to 155 km with estimated magnitudes up to 8 for the associated earthquakes. While they are typically found in northern parts of Fennoscandia, there are a number of published accounts claiming their existence further south and even in northern central Europe. This study focuses on a prominent scarp discovered recently in lidar (light detection and ranging) imagery hypothesized to be from a post-glacial fault and located about 250 km north of Stockholm near the town of Bollnäs. The Bollnäs scarp strikes approximately north–south for about 12 km. The maximum vertical offset in the sediments across the scarp is 4–5 m with the western block being elevated relative to the eastern block. To investigate potential displacement in the bedrock and identify structures in it that are related to the scarp, we conducted a multidisciplinary geophysical investigation that included gravity and magnetic measurements, high-resolution seismics, radio-magnetotellurics (RMT), electrical resistivity tomography (ERT) and ground-penetrating radar (GPR). Results of the investigations suggest a zone of low-velocity and high-conductivity in the bedrock associated with a magnetic lineament that is offset horizontally about 50 m to the west of the scarp. The top of the bedrock is found ∼ 10 m below the surface on the eastern side of the scarp and about ∼ 20 m below on its western side. This difference is due to the different thicknesses of the overlying sediments accounting for the surface topography, while the bedrock surface is likely to be more or less at the same topographic level on both sides of the scarp; else the difference is not resolvable by the methods used. To explain the difference in the sediment covers, we suggest that the Bollnäs scarp is associated with an earlier deformation zone, within a wide (> 150 m), highly fractured, water-bearing zone that became active as a reverse fault after the latest Weichselian deglaciation.

A preliminary assessment for groundwater in a part of North Central Nigeria using Landsat ETM

In a basement environment where groundwater is restricted to secondary permeability, structural analysis using remote sensing is a reliable and cheap method for the start-up process for groundwater exploration. In this study, remote sensing and GIS technology were employed as a major tool for groundwater prospecting in a part of North Central Nigeria; an area prone to water scarcity for more than half of every year. The geological map of the study area, Landsat7 ETM+, and Shuttle Radar Topographic Mission (SRTM) imageries covering the area were employed in this study. Edge enhancements and directional filtering were carried out to enhance the visibility of lineaments on the Landsat imagery. To eliminate bias and subjectivity, Normalized Difference Vegetation Index (NDVI) and Digital Elevation Model (DEM) of the study area were processed for further lineament detection. Results indicate that lineaments extracted from the Landsat imagery were in agreement with those obtained from the DEM. Those obtained from the NDVI analysis were also in agreement, except for a number of entirely new lineaments detected. This showed the importance of healthy vegetation aligned in a linear or curvilinear way as a major guide to detecting subsurface water-bearing zones that are not visible on the surface. Results also show that the dominant lineaments trend along the NE-SW direction. The northwest and central parts of the study area have relatively high lineament density, while the southern part has very low lineament density. These areas with high lineament density values are more feasible zones for groundwater prospecting. Keywords: Basement complex, Edge enhancement, Groundwater exploration, Landsat ETM+, NDVI

Matrix Permittivity Measurements for Rock Powders

Summary Formation water content is one of the key petrophysical quantities provided by dielectric logging. However, to determine water content from formation permittivity measurements, the rock matrix permittivity must be known. Uncertainty in the rock matrix permittivity values translates into uncertainty in the water-content estimate, which is especially important in low-porosity formations or complex lithologies. Matrix permittivity values are not well-known for a number of minerals and can also vary for the same type of mineral in different formations. Thus, a laboratory methodology for the accurate determination of matrix permittivity at dielectric logging frequencies is required to facilitate accurate log interpretation. One can measure matrix permittivity values on solid plugs (Seleznev et al. 2011). However, the plug-based methodology can be challenging in very-low-permeability or unconventional reservoirs because of difficulties with plug drying. In addition, it is not readily applicable to unconsolidated formations. Finally, it may be impossible to cut solid plugs because of limited availability of rock material. Matrix permittivity measurements made on rock powders are capable of addressing all these issues. We introduce a methodology for laboratory measurements of matrix permittivity on rock powders at 1 GHz. The methodology is based on conducting dielectric measurements on mixtures of rock powders and liquids with variable permittivities in a dielectric resonator. The permittivity of the rock matrix is inverted from a series of measurements obtained on pure liquids and powder/liquid mixtures. The methodology was benchmarked on a collection of samples representing common oilfield lithologies with matrix-permittivity values between 4.6 and 8.6. The reference matrix-permittivity values were first measured on solid plugs. Then, the plugs were crushed into powders, and the matrix permittivity values were determined on powders following the proposed methodology. The values obtained on powders matched the ones measured on solid plugs within 0.2 dielectric units, resulting in accuracies better than 1% for the water-filled porosity and better than 1,000 ppm for water salinity. This new methodology was applied to a number of core samples from a carbonate reservoir offshore Sarawak, where dielectric logging was performed along with conventional core analysis. The resulting measured matrix permittivity values were then used to interpret the dielectric log measurement. Results showed a better estimation of water-filled porosity and of the textural MN parameter, equivalent to the Archie's cementation exponent in a water-bearing zone, than would have resulted from using “chartbook” values of matrix permittivity. A consistent and optimized interpretation was obtained in porosities ranging from 5% to more than 30%.

Modern method for sealing deep boreholes

Deep, investigation boreholes for suitable location of radioactive repositories and holes with larger diameter for storing such waste at great depth must be effectively isolated from the biosphere. A method for sealing boreholes by use of dense smectite clay where the rock is low-permeable and has only very fine fractures, and by concrete cast where the holes intersect water-bearing fracture zones, has been used for sealing of up to 500m deep exploration boreholes in Sweden and Finland. The paper describes the practical conditions for construction of seals, and the processes that lead to the required tightness of the clay and concrete materials. Application of this technique to even deeper boreholes requires use of mud instead of water for stabilization and for moderating the rate of maturation. Placeability requires that the maturation of the initially unsaturated clay is neither too fast nor too slow and means of controlling the rate are described. The proposed concrete material has a very low cement content, and talc as fluidizer, which gives slow but ultimately very significant strengthening and low solubility of the cement reaction products. At a few kilometer depth the temperature can be more than 60°C, which has to be sustained by the sealing materials, and this makes saponite and mixed-layer smectite/illite clay possible alternatives to pure smectites. The concept is judged to be applicable also to sealing of abandoned boreholes used for fracking.

Hydrothermal alteration of clay and low pH concrete applicable to deep borehole disposal of high-level radioactive waste – A pilot study

In the very deep borehole (VDH) concept for high level radioactive waste disposal, the combined usage of clay and concrete provides an attractive way of achieving both high strength and low permeability required for sealing the various sections of the hole. The concrete is required for mechanical stability where water-bearing fracture zones are intersected, whereas the clay effectively seals sections in stable rock masses. As both the clay and concrete may be exposed to temperatures in the range of 60–150°C in various parts of the hole, there is a need to address the stability of these materials under thermally enhanced aqueous conditions. In this pilot study, a new type of organic-free, low pH concrete based on granulated blast furnace slag is tested, which is hardened and altered under hydrothermal conditions in the laboratory. The results presented show that both adequate compressive strength (up to ∼9MPa) and low hydraulic conductivity (down to ∼5.6×10−10) is attained at elevated temperatures ranging up to 150°C, indicating that clay-concrete sealing can be a successful method used to prevent radionuclides from migrating vertically up through the borehole repository.

Hydrogeophysics for Informed Water Management Decisions in the Anangu Pitjantjatjara Yankunytjatjara (APY) Lands of South Australia

The Aboriginal population of the Anangu Pitjantjatjara Yankunytjatjara (APY) lands in South Australia is dependent on groundwater for nearly all water needs. In that region, placement of wells in productive aquifers of appropriate water quality is challenging because of lack of hydrologic data and variable aquifer properties. It is desirable to have an improved ability to identify and evaluate groundwater resources in this remote region with cost-effective methods that make minimal impact on the environment. A project supported by the Society of Exploration Geophysicists program Geoscientists Without Borders tested a combined geophysical approach with airborne and ground-based data sets to locate a potential aquifer, confirm water content, and estimate the subsurface extent of the water-bearing zone. This hydrogeophysical approach was an effective means for exploration and evaluation of groundwater resources in APY lands generally, and it characterized a specific aquifer as a case study.

Hydrogeological investigation of shallow aquifers in an arid data-scarce coastal region (El Daba’a, northwestern Egypt)

Hydrogeological investigations in arid regions are particularly important to support sustainable development. The study area, El Daba’a in northwestern Egypt, faces scarce water resources as a result of reported climate change that particularly affects the southern Mediterranean coast and increases stress on the local groundwater reserves. This change in climate affects the area in terms of drought, over-pumping and unregulated exploration of groundwater for irrigation purposes. The hydrogeological investigation is based on a multidisciplinary data-layer analysis that includes geomorphology, geology, slope, drainage lines, soil type, structural lineaments, subsurface data, stable isotopes, and chemical analyses. The study area contains Pleistocene and middle Miocene marine limestone aquifers. Based on lithology and microfacies analysis, the middle Miocene aquifer is subdivided into two water-bearing zones. The area is affected by sets of faults and anticline folds, and these structures are associated with fractures and joints that increase permeability and facilitate the recharge of groundwater. Stable isotope data indicate that groundwater of both the Pleistocene and middle Miocene aquifers is recharged by modern precipitation. The high salinity values observed in some groundwater wells that tap both aquifers could be attributed to leaching and dissolution processes of marine salts from the aquifers’ marine limestone matrix. In addition, human activities can also contribute to an increase in groundwater salinity. A future water exploration strategy, based on the results from the multidisciplinary data-layer analysis, is proposed for the area. The derived scientific approach is transferable to other arid coastal areas with comparable conditions.

Laterally constrained inversion for CSAMT data interpretation

Laterally constrained inversion (LCI) has been successfully applied to the inversion of dc resistivity, TEM and airborne EM data. However, it hasn't been yet applied to the interpretation of controlled-source audio-frequency magnetotelluric (CSAMT) data. In this paper, we apply the LCI method for CSAMT data inversion by preconditioning the Jacobian matrix. We apply a weighting matrix to Jacobian to balance the sensitivity of model parameters, so that the resolution with respect to different model parameters becomes more uniform. Numerical experiments confirm that this can improve the convergence of the inversion. We first invert a synthetic dataset with and without noise to investigate the effect of LCI applications to CSAMT data, for the noise free data, the results show that the LCI method can recover the true model better compared to the traditional single-station inversion; and for the noisy data, the true model is recovered even with a noise level of 8%, indicating that LCI inversions are to some extent noise insensitive. Then, we re-invert two CSAMT datasets collected respectively in a watershed and a coal mine area in Northern China and compare our results with those from previous inversions. The comparison with the previous inversion in a coal mine shows that LCI method delivers smoother layer interfaces that well correlate to seismic data, while comparison with a global searching algorithm of simulated annealing (SA) in a watershed shows that though both methods deliver very similar good results, however, LCI algorithm presented in this paper runs much faster. The inversion results for the coal mine CSAMT survey show that a conductive water-bearing zone that was not revealed by the previous inversions has been identified by the LCI. This further demonstrates that the method presented in this paper works for CSAMT data inversion.

Geothermal Water at a Coal Mine: From Risk to Resource

Geothermal water from a Cambrian limestone aquifer presented a flooding risk at the No. 8 coal 21 mine near Pingdingshan City, China. The water-bearing zones were identified using the mine transient electromagnetic method and direct current prospecting, and a groundwater drainage system was installed. After water drainage was implemented, the water level in the limestone near the haulway dropped 17.2 m in 277 days, greatly reducing the risk of a mine water inrush. The water quality, quantity, and temperature allowed it to be used for mineral baths, resulting in energy savings and emission reductions.

Radiowave imaging research (RIM) for determining the electrical conductivity of the rock in borehole section OL-KR4−OL-KR10 at Olkiluoto, Finland

We carried out an electromagnetic cross-borehole survey as a feasibility target for the radiowave imaging method (RIM) in a possible area for the repository of spent nuclear fuel in Finland to reveal the properties of granitic, i.e. crystalline bedrock. The resistivity in the bedrock varies strongly in the range of tens to tens of thousands of ohm metres due to sulphide bearings. Because increased electrical conductivity is often associated with rock mass deformation (clay and water-bearing fractures, sulphide- and graphite-bearing zones), the obtained information could be used, for example, in determining the integrity of the rock mass.This paper describes the field work, as well as the interpretation and comparison of the results of radiowave imaging with other geophysical results in one borehole section at the 200–600 m depth level from 2005. The results verified that the method can be used to delineate and follow sulphide-bearing horizons between boreholes. The detected low and high resistivity zones and their apparent shapes and orientations are in fair agreement with geological and other geophysical results. The material properties differ from those recorded in seismic tomography from the same location, although the reflections partly describe the boundaries of domains differing in electrical properties. Using borehole geometry, similar but more detailed information is obtained than with electric and electromagnetic measurements from the ground surface. Our first experience with RIM convinced us that it can also be utilised in such challenging environments as at Olkiluoto, and not only when massive deposits exist.

A New GIS based Application of Sequential Technique to Prospect Karstic Groundwater using Remotely Sensed and Geoelectrical Methods in Karstified Tepal Area, Shahrood, Iran

In this research, recognition of karstic water-bearing zones using the management of exploration data in Kal-Qorno valley, situated in the Tepal area of Shahrood, has been considered. For this purpose, the sequential exploration method was conducted using geological evidences and applying remote sensing and geoelectrical resistivity methods in two major phases including the regional and local scales. Thus, geological structures and lithological units in regional scale have been investigated for groundwater potential. In this regard, suitable potential maps have been provided in the geographical information system (GIS) environment, using fuzzy data-driven and knowledge-driven methods. To obtain the final karstic water potential model, the prepared maps were combined using fuzzy ‘AND’ operator. In the local scale, geoelectrical surveys were conducted in the recognized high potential zones. Consequently, the results of geological investigations, analysis of lineaments extracted from satellite imagery and geoelectrical resistivity data modeling and interpretation were integrated to decide on the position of high yield extraction wells. As a result, karstic water zones in the study area were identified, and based on that, two suitable drilling locations to access and extract karstic groundwater in the study area have been suggested.

Near-surface geophysics for informed water-management decisions in the Aṉangu Pitjantjatjara Yankunytjatjara (APY) lands of South Australia

The Aboriginal population of the Aṉangu Pitjantjatjara Yankunytjatjara (APY) lands in South Australia is dependent on groundwater for nearly all water needs. In that region, placement of wells in productive aquifers of appropriate water quality is challenging because of lack of hydrologic data and variable aquifer properties. It is desirable to have an improved ability to identify and evaluate groundwater resources in this remote region with cost-effective methods that make minimal impact on the environment. A project supported by the Society of Exploration Geophysicists program Geoscientists Without Borders tested a combined geophysical approach with airborne and ground-based data sets to locate a potential aquifer, confirm water content, and estimate the subsurface extent of the water-bearing zone. This hydrogeophysical approach was an effective means for exploration and evaluation of groundwater resources in APY lands generally, and it characterized a specific aquifer as a case study.

Evaluation of Gas Reservoir of the Meghna Gas Field, Bangladesh Using Wireline Log Interpretation

The gas reservoir from the well Bakhrabad-09 of the Meghna Gas Field, Bangladesh was evaluated in this study in order to appraise the qualities of the reservoir based on quantitative analysis of petrophysical parameters. Among 24 permeable zones, two zones were gas-bearing and rests were water-bearing zones which identified in the study well. Relatively high resistivity, high SP log, low gamma ray log, very low neutron and low density log responses indicate hydrocarbon type might be gas-bearing zones than that of water-bearing zones. The shale volume of those zones ranged from average 21% to 22 % indicated that shaly sand dominating lithology and less affect the water saturation values in the gas reservoir. The average porosity of these zones ranged from 31% to 34 % which was within the limit for good hydrocarbon accumulation. Three saturation equations were used to evaluate the water saturation which was converted to gas saturation. The average gas saturation values of these zones were more than 60 % indicate high hydrocarbon accumulation. The average permeability of these zones ranged from 42.5 md to 50 md respectively which was within ranged for commercial gas accumulation. Average bulk volume of water ranged from 0.045 to 0.053 was shown that the reservoir consist of mainly fine to very fine grained sandstone and more or less at irreducible water state. It can be concluded that gas reservoir are good qualities for commercial hydrocarbon accumulation and production. erroneous values for water saturation and porosity in the presence of shale effect. The determinations of reservoir quality and formation evaluation processes are largely depend on quantitative evaluation of petrophysical analysis. Petrophysical analysis of gas reservoir of different gas field was carried out by Islam et al. (3-7) in Bengal Basin, Bangladesh. Rahman et al. (8) was carried out the analysis of reservoir sand of Titas-15 well using well log interpretation. In this regard, the study was focused on the gas reservoir evaluation in the well Bakhrabad-09 of Meghna Gas Field, Bangladesh using wireline log interpretation. The objective of the study is to identify the gas zones of reservoir using composite log responses and to determine petrophysical parameters of the gas reservoir of the Meghna Gas Field, Bangladesh. It is located in Bancharampur upzila under Brahmanbaria District some 40 km away of northern most east direction from capital city of Dhaka, Bangladesh. Meghna Gas Field was discovered by BAPEX in 1990 (9) (Figure 1).

Basal water-bearing zone of the oil-sands deposits of the Cretaceous McMurray Formation at Christina Lake, Alberta, Canada

The Cretaceous McMurray Formation at Christina Lake in Alberta, Canada contains bitumen-rich sand bodies in the lower part. These sand bodies were deposited in lowstand fluvial systems with the onset of relative sea-level rise in the Western Canada foreland basin, forming thick interconnected bodies along the paleovalley. Oil recovery from these reservoirs commonly suffers from bottom water, which reduces not only pay thickness but also the efficiency of thermal recovery processes. For successful oil production in this area, basal water-bearing zone should be investigated and incorporated in determining optimistic well locations and operational strategies. Examination of 455 wireline logs reveals a widespread water-bearing zone at the basal part of the McMurray Formation at Christina Lake. The basal water-bearing zone is relatively thick on paleotopographic lows, particularly along the paleovalley. This result suggests that paleotopography played a crucial role in the distribution of the basal water-bearing zone.

Interpretation of hydraulic rock types with resistivity logs in Tertiary deepwater turbidite reservoirs: Pore-scale modeling verified with field observations in the Gulf of Mexico, USA

Well-log-based hydraulic rock typing is critical in deepwater reservoir description and modeling. Resistivity logs are often used for hydraulic rock typing due to their high sensitivity to rock textural attributes such as porosity and tortuosity. However, resistivity logs measured at different water saturation conditions need to be cautiously used for hydraulic rock typing because, by definition, the properties of hydraulic rock types (HRT) are independent of fluid saturation. We compare theoretical models of electrical and hydraulic conductivity of clastic rocks exhibiting different pore-size distributions and originating from different sedimentary grain sizes. When rocks exhibiting similar porosity ranges are fully saturated with high-salinity water, hydraulic conductivity is dominantly controlled by characteristic pore size while electrical conductivity is only marginally affected by the characteristic pore size. As a result, rock types with similar porosity but different characteristic pore sizes cannot be effectively differentiated with resistivity logs in a water-bearing zone. In a hydrocarbon-bearing zone at irreducible water saturation, capillary pressure gives rise to specific desaturation behaviors in different rock types during hydrocarbon migration, thereby causing differentiable resistivity log attributes that are suitable for classifying HRT. Core data and well logs acquired from a deep-drilling exploration well penetrating Tertiary turbidite oil reservoirs in the Gulf of Mexico, verify that inclusion of resistivity logs in the rock classification workflow can significantly improve the accuracy of hydraulic rock typing in zones at irreducible water saturation. Classification results exhibit a good agreement with those obtained from nuclear magnetic resonance logs, but have relatively lower vertical resolution. The detected and ranked HRT exhibit different grain-size distributions, which provide useful information for sedimentary facies analysis.

New approach to hydrogeological modelling and source data collecting in a small mountainous hard rock basin – experiences from the Sudetes Mts. (SW Poland)

We demonstrate a new research methodology into flow paths and groundwater resources with in small hard rock basins , where little hydrogeological data is available, a picture may be obtained by modeling. Data has been collected in the Złoty Potok river catchment (area 4.4 sq km), located in the eastern Sudety Mts. (SW Poland). The study area, as for most small hard rock basins in the Sudety Mts. is characterized by: i) steeply sloping terrain, ii) a complex flow system connected to several media, ii) poorly constrained hydrogeological parameters. In such conditions, groundwater models are difficult to implement. To overcome these difficulties, we applied a concept of mixed flow ruled by laws of Darcy (porous media) and Hagen-Poiseuille (fractured media), and the concept of three water-bearing zones, a classic solution for scales of above several sq km, combined with a discrete fracture model. Field data applied for modeling were collected over one year, measuring all manifestations of groundwater occurrence: i) effective infiltration (lysimeter), ii) fracture mapping, iii) stream flow and flow disappearance. As a result of modelling, specific flow domains were identified; which form a system of zones, characterized by different geometries and flow velocities. A new, previously unrecognized zone of considerable importance for water extraction, i.e. fractures in the river valley axis, reaching a deep part of the orogen (up to 300 m b.g.l.) was defined. The relationships investigated allowed prepation of a prognosis for deep groundwater intake locations in poorly described mountainous areas. The success of the solutions obtained in this typical mountainous river basin suggests that this method may be come efficiently and widely used in other hard rock areas. The research undertaken offers an innovative, efficient approach to groundwater resource assessment in hard rock.

Geoelectrical Schlumberger investigation for characterizing the hydrogeological conditions using GIS in Omalur Taluk, Salem District, Tamil Nadu, India

The increasing demand for freshwater has necessitated the exploration for new sources of groundwater, particularly in hard rock terrain, where groundwater is a vital source of freshwater. A fast, cost effective, and economical way of exploration is to study and analyze geophysical resistivity survey data. The present study area Omalur taluk, Salem District, Tamil Nadu, India, is overlain by Archaean crystalline metamorphic complex. The study area is a characteristic region of unconfined aquifer system. The potential for occurrence of groundwater in the study areas was classified as very good, good, moderate, and poor by interpreting the subsurface geophysical investigations, namely vertical electrical soundings, were carried out to delineate potential water-bearing zones. The studies reveal that the groundwater potential of shallow aquifers is due to weathered zone very low resistivity and very high thickness and the potential of deeper aquifers is determined by fracture zone very low resistivity and very high thickness area. By using conventional GIS method, the spatial distribution maps for different layer (top soil, weathered zone, first fracture zone, and second fracture zone) thicknesses were prepared. The geoelectrical approach was successfully applied in the study area and can be therefore easily adopted for similar environments.

The use of magnetic and geo-electrical data to delineate the subsurface structures and groundwater potentiality in Southeastern Sinai, Egypt

The study area is located in the southern part of Sinai Peninsula. This study was done to delineate the subsurface structure of the basement rocks affecting the groundwater potentiality in the study area and to perform the lateral and vertical variations in the subsurface lithologic properties. To achieve these, a high-resolution total intensity magnetic map and geo-electrical survey were acquired. Two-dimensional power spectrum, analytical signal, and Euler deconvolution techniques are applied on magnetic data. The geo-electric data interpretations concluded that, the study area can be classified into five units of sediments arranged as: (1) the top surficial layer of dry sand and gravels; (2) the second layer of silty sand layer with thickness ranging from 5 to 35 m; (3) the third layer of dry sand with thickness ranging from 5 to 130 m; (4) the fourth layer composed of saturated sand which was considered as the water-bearing zone of the investigated interval, its thickness ranges between 50m and more than 200 m; (5) the fifth layer is interpreted as basement rocks. The depth to the basement surface has an average value of 156 m at the eastern side and 758 m at the western side of the study area. This area is characterized by a graben structure bounded by major faults striking in the NW–SE direction and is considered one of the most promising regions for water resources in Sinai.