Nubian Sandstone Research Articles

Hydro-Geochemistry and Water Quality Index Assessment in the Dakhla Oasis, Egypt

Water quality is crucial to the environmental system and thus its chemistry is important, and can be directly related to the water’s source, the climate, and the geology of the region. This study focuses on analyzing the hydrochemistry of specific locations within the Dakhla Oasis in Egypt. A total of thirty-nine groundwater samples representing the Nubian Sandstone Aquifer (NSSA) and seven surface water samples from wastewater lakes and canals were collected for analysis. Key parameters such as pH, electrical conductivity (EC), and total dissolved solids (TDS) were measured on-site, while major ions and trace elements (Fe+2 and Mn+2) were analyzed in the laboratory. The water quality index (WQI) method was employed to assess the overall water quality. Hydro-chemical facies were investigated using Piper’s, Scholler’s, and Stiff diagrams, revealing sodium as the dominant cation and chloride, followed by bicarbonate as the dominant anion. The hydro-chemical composition indicates that Na–Cl constitutes the primary water type in this study. This points to the dissolution of evaporates and salt enrichment due to intense evaporation resulting from the region’s hyper-aridity. In groundwater samples, the order of hydro-chemical facies is HCO3− > Cl− > SO4−2 > Na+ > Ca+2 > K+ > Mg+2, while in wastewater samples, it is Cl− > Na+ > SO4−2 > HCO3− > Ca+2 > Mg+2 > K+. When considering iron and manganese parameters, the water quality index (WQI) values suggest that most groundwater samples exhibit excellent to good quality but become poor or very poor when these elements are included. This study could prove valuable for water resource management in the Dakhla Oasis.

Enhanced geological and radioactive mapping of Gabal Abu Ashayir-Gabal El Bakriyah area, central Eastern Desert, Egypt, using remotely sensing data

AbstractThe primary goal of this work is to integrate airborne gamma-ray spectrometry with multispectral data from ASTER and Landsat-8 for mapping of the geology, radiometric data, and types of alterations of Gabal Abu Ashayir-Gabal El Bakriyah area, central Eastern Desert, Egypt. Utilizing various image processing techniques like color band composites (CBC), principal component analysis (PCA), band ratios (BR), and minimum noise fraction (MNF), it is possible to map the hydrothermal alterations zones and identify the lithological units under investigation. By identifying the various lithological units and alteration types, these results are validated and verified in the field. These methods’ outputs are combined to create an accurate geological map of the research region and tracing the propylitic, phyllic and iron oxy-hydroxides alterations. These rock units are ophiolitic mélange (oldest), arc metavolcanics, arc granitoids, younger gabbro, late-collision granites (monzogranites, syenogranites and alkali feldspar granites) and Nubian Sandstone (Taref formation and Quseir Formation) youngest, Furthermore, the radioactive anomalies are primarily associated with ferrugination zones (iron oxy-hydroxides alteration) at Gabal El Bakriyah monzogranite and alkali feldspar granite. The radioactive minerals are uranothorite, thorite and fergusonite. The opaque minerals that encountered at the rock units of Gabal Abu Ashayir-Gabal El Bakriyah are chromite, ilmenite, magnetite, chalcopyrite and chalcocite, whereas the non-opaque minerals comprises titanite, rutile, fluorite, garnet, zircon, apatite and barite.

Application of magnetic data and satellite spectral imaging in identifying gold mineralization zones and its associated subsurface structures at Fawakheir-Attala area, Central Eastern Desert, Egypt

The Fawakheir-Attala gold mining zone in Egypt’s Central Eastern Desert features a diverse range of rock formations, including Precambrian crystalline rocks and Phanerozoic sedimentary formations. These formations encompass gneisses, metavolcanics, metasediments, a metagabbro-diorite complex, Dokhan volcanic rocks, and granitic rocks, alongside lower and upper Nubia sandstones. Faults and shear zones are pivotal in controlling gold mineralization within the area, indicative of substantial mineral wealth. This study aimed to map subsurface structural characteristics and investigate gold mineralization zones using aerial magnetic data and ASTER remote sensing, the latter of which played a crucial role in highlighting the surface exposure of alteration zones. Geological surveys combined with remote sensing techniques were employed to identify rock types and mineralization zones, while magnetic methods, including aeromagnetic surveys and ground-based studies, were used to reveal underlying structural properties and fault systems. Analysis of aeromagnetic data revealed a large mineralization zone running from the Fawakhir Gold mine through the Attala Gold mine in a NW–SE direction. Various structural trends and faults, including NW–SE, NE–SW, E–W, and N–S directions, were identified, strongly associated with hydrothermal alteration zones and gold mineralization. Shallow basement relief was observed in the eastern and central regions, contrasting with deeper formations and greater relief in the western section. Land magnetic surveys were utilized to identify new areas for gold mineralization, with geochemical analysis confirming gold content in quartz veins and host rocks. The integration of magnetic and remote sensing techniques effectively highlighted alteration zones indicative of potential mineralization, which could have a subsurface continuation, aiding in the identification of gold occurrences connected to faults, lineaments, and mineralization zones.

Unveiling the Dynamics and Sustainability of the Nubian Aquifer System in El-Marashda, Egypt Through Geophysical, and Hydrogeochemical Investigations

AbstractThis research investigates the geophysical, hydrogeochemical, and geological characteristics of the Nubian Aquifer System in the El-Marashda area, located beneath the Eastern Sahara Desert in northeastern Africa. The primary objective is identifying the aquifer geometry, assessing groundwater quality, and evaluating environmental pollution levels. A Magnetotelluric survey was employed to examine the subsurface geological composition and electrical resistivity characteristics of the aquifer system. The study revealed a freshwater-saturated Nubian Sandstone layer at depths between 986 and 1009 m with resistivity values of 101 to 182 Ohm.m, indicating a substantial and potentially sustainable groundwater resource. Overlying limestone and Marly Limestone layers influence the aquifer’s permeability and storage capacity. The chemical analysis of water from three wells showed suitability for drinking and irrigation, with no sodium and magnesium levels hazards. The Heavy Metal Pollution Index (HPI) and Heavy Metal Evaluation Index (HEI) indicated low to medium contamination, posing potential environmental health risks. Human health risk assessments using USEPA methodology found acceptable non-carcinogenic risks, with Hazard Quotients (HQs) for heavy metals below 1 and a negligible Hazard Index (HI). The comprehensive investigation underscores the potential for sustainable groundwater utilization in El-Marashda. It highlights the aquifer’s suitability for irrigation, with low contamination levels and minimal health risks. These findings provide a foundation for informed and sustainable water resource management, environmental protection, and resilient infrastructure development in the region. The methodologies and results align with global standards, demonstrating their applicability in globally diverse geological contexts. This research contributes valuable baseline data for future studies and monitoring efforts, whether at local or global sites, emphasizing the importance of continued investigation to ensure sustainable groundwater management.

Metabolic adaptations underpin high productivity rates in relict subsurface water

Groundwater aquifers are ecological hotspots with diverse microbes essential for biogeochemical cycles. Their ecophysiology has seldom been studied on a basin scale. In particular, our knowledge of chemosynthesis in the deep aquifers where temperatures reach 60 °C, is limited. Here, we investigated the diversity, activity, and metabolic potential of microbial communities from nine wells reaching ancient groundwater beneath Israel’s Negev Desert, spanning two significant, deep (up to 1.5 km) aquifers, the Judea Group carbonate and Kurnub Group Nubian sandstone that contain fresh to brackish, hypoxic to anoxic water. We estimated chemosynthetic productivity rates ranging from 0.55 ± 0.06 to 0.82 ± 0.07 µg C L−1 d−1 (mean ± SD), suggesting that aquifer productivity may be underestimated. We showed that 60% of MAGs harbored genes for autotrophic pathways, mainly the Calvin–Benson–Bassham cycle and the Wood–Ljungdahl pathway, indicating a substantial chemosynthetic capacity within these microbial communities. We emphasize the potential metabolic versatility in the deep subsurface, enabling efficient carbon and energy use. This study set a precedent for global aquifer exploration, like the Nubian Sandstone Aquifer System in the Arabian and Western Deserts, and reconsiders their role as carbon sinks.

Structural assessment and petrophysical evaluation of the pre-Cenomanian Nubian sandstone in the October Oil Field, central Gulf of Suez, Egypt

The low quality of the seismic resolution of the studied Cambrian Pre-Cenomanian formations, which rest directly on the basement in the October Field in the Gulf of Suez, requires study, and the structure pattern controlling these formations is uncertain. The poor quality of the seismic data resolution in the Gulf of Suez is due to the presence of thick sequences of evaporites represented by the South Gharib and Zeit formations. Therefore, the current study used seismic reflection data integrated with well-log data to define the structural-stratigraphic setting of the pre-Cretaceous Nubian reservoir sequence. The study aims at locating and delineating zones having excellent reservoir potential within the Nubian sequence horizons (Nubian Transition, main Nubian, Nubian marker-1, and Nubia marker-2, referred to as NT, MN, M1 and M2, respectively) through the integration of the 3D static modelling and the petrophysical parameters deduced from the well-log data processing. A detailed petrophysical analysis, based on the wireline logs of some wells, was performed to determine the lithological units using two types of cross plots (Neutron-Density and M-N plots), and the different petrophysical parameters that characterize the various Nubian horizons were also computed. 3D modelling was used to visualise the lateral and vertical changes of the reservoir characteristics. The seismic mapping reveals that the Nubian structure is controlled by an NW-SE trending (Clysmic trend) of an NE-plunging asymmetrical anticlinal feature unconformably resting on a basement horst. The main structure is affected by two major normal faults, which trend NW, andis cut by two smaller sub-parallel faults that disturb the core of the structure, which is unaffected by the easterly oriented faults of the Aqaba trend. The petrophysical analyses indicate that the Nubian sandstones have intervals of good reservoir quality, with a total net-pay thickness of about 500 m, net sand ratios (60–90 %), effective porosity (10–25 %), and hydrocarbon saturation (85%), which may encourage further drilling, especially in the southeast portion. The result of this study can be extended to the other Nubia sandstones resting on the basement complex in the Gulf of Suez.

Optimization of floodwater redistribution from Lake Nasser could recharge Egypt’s aquifers and mitigate its excessive floods

Extreme precipitation periods, possibly related to climate change, over the Nile River source areas caused flooding in Sudan and excess runoff reaching Lake Nasser in Egypt in 1998–2002 and 2019–2022. Excess water from the 1st event (25.5 × 109 m3) was channeled to depressions within the plateau west of the Nile Valley, forming the Tushka Lakes, where it was left to evaporate, a fate that awaits the 53.5 × 109 m3 from the 2nd event while the underlying fossil Nubian Sandstone Aquifer System is being depleted (−0.98 × 109 m3/yr). We simulated release scenarios of excess Lake Nasser waters (53.5 × 109 m3) to proximal lowlands; preference was given to the scenario that recharged the aquifer through infiltration (74.3%) and minimized losses to evaporation (20.1%) and surface runoff (5.6%). Findings serve as an example of adaptations that replace catastrophic consequences of climate change with beneficial and sustainable development opportunities.

Modeling and analysis of temporal dynamics in groundwater aquifers of New Valley Oases, Egypt

Water scarcity poses a significant challenge in arid and semi-arid regions, necessitating a focused exploration of groundwater resources. Egypt, confronted with various water challenges, particularly in its Western Desert, relies heavily on groundwater as the exclusive water source due to the presence of the Nubian Sandstone aquifer. Effective groundwater management in this region is imperative. This study delves into the hydrogeological characteristics of the Nubian Sandstone aquifer system (NSAS) in the prominent New Valley Oases—Kharga, Dakhla, and Farafra—where agricultural activities heavily depend on groundwater. The primary objective entails a meticulous temporal assessment of the impact of groundwater development on aquifer behavior, groundwater levels, and drawdown. Employing a remote sensing approach, agricultural expansion from 1995 to 2020 was scrutinized. The Visual MODFLOW package served as a robust tool for simulating groundwater flow in the study areas. Noteworthy findings reveal an upward trajectory in agricultural crop areas, escalating by approximately 6% from 1740 km² in 1995 to 1850 km² in 2020. Concurrently, drawdown, influenced by current groundwater extraction, is anticipated to range from 0.5 to 5 meters per year. To ensure the sustainable development of these areas, stringent regulations must be implemented, underscoring the imperative for judicious groundwater management practices. This research underscores the critical need for informed decision-making and proactive measures to address the evolving dynamics of groundwater resources in the New Valley Oases.

Utilization of abandoned oil well logs and seismic data for modeling and assessing deep geothermal energy resources: A case study

Hammam Faraun (HF) geothermal site in Egypt shows potential for addressing energy demand and fossil fuel shortages. This study utilizes abandoned oil well logs, seismic data, and surface geology to assess HF geothermal energy resources.Seismic interpretation identified a significant clysmic fault parallel to Hammam Faraun fault (HFF), named CLB fault. The two faults together create a renewable geothermal cycle through circulation of mixed formation-sea waters.Petrophysics revealed two main geothermal reservoirs: the Nubian sandstone reservoir and the Eocene Thebes carbonate reservoir with water saturation values approaching 100 %. Corrected borehole temperatures indicated reservoir temperatures around 120 °C and 140 °C for the Thebes and Nubian reservoirs, respectively.Fracture analysis and stress state provided insights into subsurface fractures. A geomechanical model demonstrated the impact of different stresses and pore pressure on geothermal fluid flow. NE-SW oriented fractures showed a higher dilation tendency due to aquathermal expansion.The integrated conceptual geothermal model suggested a magma chamber beneath HF as the heat source, related to Oligo-Miocene volcanic activity. The breached relay ramp and fault-related open fracture system serve as pathways for geothermal fluids.Evaluation of the geothermal potential utilized volumetric calculations and Monte Carlo simulation. The estimated hot water volumes were 1.72 km3, 4.242 km3, and 5.332 km3 for the Nubian reservoir in the onshore part, Thebes reservoir in the offshore part, and Nubian reservoir in the offshore part, respectively.The results indicate a medium enthalpy resource suitable for electricity generation using a Kalina geothermal power plant. The predicted geothermal power output is promising, with an average power output of 9.64 MWe, 21.38 MWe, and 43.76 MWe for the Nubian reservoir in the onshore part, Thebes reservoir in the offshore part, and Nubian reservoir in the offshore part, respectively. These outputs can potentially supply electricity to approximately 12,000, 29,000 and 53,000 households, respectively.

Use of remote sensing, spatial and geophysical modeling, and real recharging capabilities to identify suitable areas for groundwater exploitation in dry coastal areas

Accurate identification of groundwater potential areas in arid regions is an important task for groundwater management and sustainability. As a result, this study used the innovative integration of remote sensing (RS), geographic information system (GIS), watershed modeling system (WMS), geophysical survey, and water mass balance equation to identify potential groundwater areas in the W. Dara, Eastern Desert, Egypt. A weighted spatial probability model (WSPM) of groundwater potential based on eight regulatory factors was implemented within ArcGIS software. Drainage density (DD), precipitation (P), net groundwater recharge (NGR), terrain slope (TS), lineament density (LD), lithologic group (LG), water quality (TDS), and depth to groundwater level (DGW) are the aspects considered. The Analytical hierarchy process (AHP) method was used to assign weights to these parameters, and their accuracy was estimated using the consistency ratio (CR). The resulting groundwater potential map classified W. Dara study area into five categories, ranging from very low to very high potential. A geophysical survey, in the form of Vertical Electrical Sounding (VES) and Transient Electromagnetic (TEM), was conducted along W. Dara to validate the results of the WSPM, which identified areas of high groundwater potential. The 1D inversion of VES/TEM shows that the central and western parts of W. Dara are considered the most promising areas for groundwater occurrence, and are located in areas of high and very high potential classes derived from WSPM. Moreover, the results of VES and TEM surveys showed that the proposed aquifers (Nubian Sandstone, Miocene, and Quaternary) in the study area are horizontally and vertically connected through a set of normal faults traversing NW-SE. Ten sites have been proposed for drilling additional exploitative wells in W. Dara area based on the WSPM and geophysical survey with the aim of sustainable development. Thus, the integrated techniques applied in this study proved effective in accurately determining the development strategy for arid and semi-arid coastal areas, especially those that suffer from scarcity of rainfall and increased agricultural reclamation requirements in remote areas.

Carcinogenic and Non-Carcinogenic Health Risk Evaluation of Heavy Metals in Water Sources of the Nubian Sandstone Aquifer in the El-Farafra Oasis (Egypt)

Expanding anthropogenic activities, globally and in Egypt, have increased concentrations of heavy metals in surface and ground waters. Contamination of drinking water may threaten public health. In the present study, the concentrations of 10 heavy metals were analyzed from natural springs (6) and drilled wells (10) in the Nubian Sandstone Aquifer of the El-Farafra Oasis and the White Desert National Park, Egypt. The average concentrations of heavy metals were in most cases below critical values of the WHO drinking water standard, except for Fe and Mn (average values were 495 and 107 µg·L−1, respectively). There is a surface circulation that develops within limestone (Post-Nubian Aquifer System—PNAS) and feeds the springs, while the water present in the wells (at least for the deeper ones) comes from the ferruginous sandstone (Nubian Sandstone Aquifer System—NSAS). This double circulation could account for the differences in the EC and TDS values (typical of a circulation in limestone-type aquifers for springs) and the Fe and Mn enrichment coming from the ferruginous sandstone of the NSAS. The average chronic daily intake (CDI) values for heavy metals in the study area are listed in decreasing order in the following: Fe > Mn > Zn > Co > Ni > Cr > As > Pb > Co > Cd. The total hazard quotient (HQtotal = HQoral + HQdermal) and Hazard Index (HI) values calculated for different heavy metals were well below the acceptable limit, indicating no significant non-carcinogenic health risks to the residents of both areas via oral and dermal absorption of drinking water. Furthermore, the results obtained for the total risk to human health showed that oral ingestion is the major pathway. Carcinogenic risk analysis indicated that the Incremental Lifetime Cancer Risk (ILCR) values for Pb, Cd, Ni, and Cr were well below the acceptable limits.

Sandstones and red beds in the Lower Cretaceous Sidi Aich Formation, Chotts Basin (Southern Tunisia): facies, architecture and depositional environments

Abstract The Lower Cretaceous deposits of North Africa represent a terrestrial to shallow-marine sandstone-dominated succession often referred to as the ‘Continental Intercalaire’ and Nubian Sandstone informal groups. The upper Barremian Sidi Aich Formation of the Continental Intercalaire is distinguished throughout the Chotts basin of southern Tunisia by sandstone-dominated sequences within conglomerate, calcareous siltstone and palaeosol red bed occurrences. This paper aims to highlight: (1) the facies distribution, internal architecture and depositional environment of the sandbodies; and (2) the origin, spatial distribution and architecture of the red beds that underlined and topped sandbodies. Strata in the Zimlet El Beida anticlinal structure, Chotts basin, offer a good opportunity for detailed field observations and bed-by-bed logging of three representative lithostratigraphic sections. Detailed sedimentological investigation allows the recognition of several lithofacies grouped into three facies associations indicating tidal flat, tidal channel and tidal bar depositional settings characterizing a transgressive tide-dominated estuarine system that developed during an episode of relative sea-level fluctuations in the Early Cretaceous. The high-resolution petrographic, mineralogical and geochemical analyses of the red beds allow the differentiation of three distinct lithofacies sets including: (1) intraformational conglomerates; (2) calcareous siltstones; and (3) palaeosol. Major red beds comprise detrital grains inherited from the host or parent sediment and authigenic minerals (dolomite, calcite and hematite) precipitated during the diagenetic processes. Grain components have been partially or completely cemented and/or replaced by terrestrial phreatic dolomite. The negative δ 13 C and δ 18 O signatures of the dolomite analyses indicate that the dolomitization processes have been influenced by fluctuations of the groundwater table or climate change from semi-arid to semi-humid conditions. This study, therefore, may provide useful data for the better understanding of the internal architecture of the red beds associated with sandbodies that represent the main and significant potential reservoir within the Lower Cretaceous Continental Intercalaire sandstone-dominated groundwater aquifers of the Chotts basin.

Geophysical appraisal and hydrocarbon potential of the Pre-Cenomanian and Miocene reservoirs in the onshore and offshore Gulf of Suez Basin

The purpose of this study is to geophysically assess the petroleum potential of the Pre-Cenomanian (Nubia sandstones) as well as the Miocene oil reservoirs in the Rabeh field and Edfu-Saqqara field, located in the Gulf of Suez Basin. This will serve as a supplementary source for future exploration in the onshore and offshore Gulf of Suez Basin. This research utilizes the wireline logs of twelve drilled wells, eight of them drilled in Rabeh field, onshore southern Gulf of Suez Basin (RE-8, RE-22, RE-25, RE-2, RE-4, Nageh-1, South Malak-1 & Tawoos-1) and the rest four wells (Edfu A-3, Edfu A-5A, GS323-1 A & GS323-4 A) drilled in Edfu-Saqqara field, offshore central Gulf of Suez Basin. Moreover, twenty seismic profiles covering the Rabeh field were structurally interpreted. This interpretation exposed that the basement rocks are severely intersected by numerous NW–SE normal faults, along with minor E–W faults. The presence of these faults has a great role in forming suitable structural traps for holding hydrocarbon. Based on the qualitative and quantitative appraisal of the well logging data, Nubia, Nukhul and Rudies formations display positive petrophysical signs for being a potential reservoir in the studied fields. These reservoirs display respectable net pay thickness varying between 21 and 550 ft (i.e. 6.5–166.5 m), good net-to-gross ratio (0.01–0.90), excellent effective porosity (0.12–0.20), little shale content (0.03–0.20), minor water saturation (0.05–0.40) and high hydrocarbon saturation (0.60–0.95). The created lateral distribution maps for the considered petrophysical parameters in the Rabeh Field suggest that the drilling efforts should be essentially directed in the southeastern side of the Rabeh field to access the high-quality Nubia sandstone reservoirs.

Integrated stratigraphical, hydrogeochemical, and geophysical studies to characterize the shallow groundwater aquifers in Wadi Araba area, western Gulf of Suez, Egypt

The construction of the New Galala City besides great mining (e.g., konoozmisr) and Seawater Reverse Osmosis Desalination Plant projects in the semiarid Gulf of Suez region of Egypt increases the demand for groundwater resources. So, the current research provides integrated stratigraphical, hydrogeochemical, and geophysical studies to investigate the shallow groundwater aquifers in Wadi Araba area on the western side of the Gulf of Suez. The stratigraphic column starts with pre-Cambrian basement rocks which are non-conformably overlain by sedimentary succession of Phanerozoic Erathem. A detailed land magnetic profile has been conducted and processed to estimate the aquifer’s geometrical parameters. This includes the subsurface spatial extension and thickness to delineate the prevailed subsurface structures in the study area. Lithostratigraphically, these aquifers are represented by the Paleozoic- lower Cretaceous siliciclastic-dominated sediments of the Nubia Group and fractured carbonate-dominated facies of the upper Cretaceous Galala Formation. Lithological characters, sedimentary facies (fluvial to shallow and open marine), microfacies types, and diagenesis processes (e.g., compaction, cementation, dissolution, and fracturing) are the main factors that affect the quality of the shallow aquifers in the study area. The main microfacies of the studied aquifers are quartz arenite, subarkose, sublitharenite, mudstone/wackestone, and packstone/grainstone. These facies are characterized by different primary and secondary porosities. According to the water sampling standard methods, nineteen groundwater samples were collected from the available hand-dug wells and springs from the Nubian sandstone aquifer and the Upper Cretaceous aquifer, respectively. Inductively coupled plasma–mass spectrometry (ICP–MS), titration, spectrophotometer and a flame photometer were used to obtain a complete chemical analysis. The results of hydrochemical analyses indicated that total dissolved solids (TDS) and concentrations of major ions as well in the lower Cretaceous aquifer increase toward the Gulf of Suez and in general higher than that of springs of the Upper Cretaceous Aquifer. The predominant factors influencing groundwater chemistry include seawater intrusion, evaporation, mineral alteration, dissolution of fossils, and ion exchange. Groundwater in the study area is unsuitable for drinking except in one sample and moderately suitable for irrigation with caution for higher salinity in samples located near the Gulf of Suez.

Application of stable isotopes, mixing models, and K-means cluster analysis to detect recharge and salinity origins in Siwa Oasis, Egypt

Waterlogging, soil salinization, and groundwater depletion in non-rechargeable aquifers are among the causes endangering the sustainability of Siwa Oasis. The water resources include the tertiary carbonate aquifer (TCA), Nubian sandstone aquifer (NSSA), springs, drains, and hypersaline lakes. Geophysical logs were used to identify various aquifer systems. Stable isotopes, major ions, and heavy metals were examined. K-means cluster analysis based on principal component analysis (PCA), hydrochemistry, stable isotopes, and mixing models using NETPATH were applied in order to understand the complex hydrogeological conditions in the different aquifer systems. The results showed that all water samples were under-saturated (SI < 1) with respect to anhydrite, halite, and gypsum minerals, indicating the water's ability to dissolve more from these minerals and increase water salinity.In contrast, calcite, dolomite, Ca-montmorillonite, and illite minerals were supersaturated in most water samples (SI > 1), showing their ability to precipitate these minerals. There is no recharge for the aquifer systems, and all the groundwater resources have paleo meteoric origin, where the maximum values of δ18O and δ2H are −8.45 and −65.63, respectively. All of the springs originated from the TCA, as indicated from the K-mean cluster analysis. There is a rapid increase in the water salinity of the TCA from 1998 to 2022 due to evaporation, rock weathering, mixing with old trapped sea water, and seepage of saline water from salt lakes. The significant variations in the water salinity of the TCA aquifer are due to the mixing between fresh water of NSSA (dilution) and salt water from Zeituna and Siwa lakes through downward flow in some locations, where over-extraction of water for irrigation purposes has decreased the water pressure in the TCA. The mixing model confirmed salt lakes' contribution in increasing the TCA salinity by 2%–4%. Mixing water from TCA and NSSA could be the best management of the water resources in Siwa Oasis, as well as the application of subsurface drip irrigation.

Geochemical and Isotopic Constraints on the Recharge and Salinization Origin of Groundwater Aquifers in El Rina–Nihayaat, South Sinai, Egypt

The Sinai Peninsula is located in the arid regions of Egypt where groundwater is the sole source for drinking and irrigation and future development. Regular assessment of the geochemical processes governing the groundwater quality is important in arid regions and paleo-aquifers. This research focuses on investigating the groundwater sustainability of the Upper Cretaceous Aquifer (UCA) located at El Rina–Nihayaat area, Southwestern Sinai Peninsula. The study aims to evaluate the main source of groundwater recharge and investigate factors deteriorating groundwater quality. The study is based on the geochemical and isotopic analyses of 31 groundwater samples tapping the UCA. The groundwater flows toward the Gulf of Suez. The groundwater salinity ranges from 1078 mg/L to 13090 mg/L indicating brackish to saline water. Two main water types have been delineated: Cl-Na and Cl-Ca indicating the final stage of groundwater evolution and leaching and dissolution of aquifer matrix of marine origin. The spatial distribution of the groundwater salinity and major ions (Na+, K+, Ca2+, Mg2+, SO42-, and Cl-) increase toward the Gulf which coincides with the direction of the groundwater flow, while bicarbonate increases toward the upstream watershed. Most of the groundwater samples tapping the UCA are depleted with the isotopic content of the stable isotopes where they range from -4.43 ‰ to -6.37 ‰ for δ18O and -28.3 ‰ to -40.2 ‰ for δ2H. The groundwater samples are depleted relative to the recent rainwater and enriched to the Nubian Sandstone located underneath the UCA indicating mixing from both source(s). The mixing estimated percentages from the recent rainwater using calibrated geochemical NETPATH model range between 48.6% to 88.5% while the upward Leakes from the Nubian water ranges between the recent rain and the paleo-Nubian water ranges between 48.6 % and 88.5 % from the meteoric rainwater, while the upwelling recharge from the paleo-Nubian groundwater ranges between 11.5 % to 51.4 %. The factorial analyses indicate three main factors governing the geochemistry of groundwater in the UCA: including water-rock interactions, meteoric recharge from annual precipitation, and upward leakages from the underneath paleowater. &#x0D; Further exploration for the UCA is recommended to determine the promising zones receiving a considerable amount of the recent rainfall.

Infiltration and recharge dynamics in the Nubian Sandstone Aquifer System of northern Chad

The Nubian Sandstone Aquifer System (NSAS) is one of the world’s largest fossil groundwater resources. In northern Chad, notably in the areas of the Tibesti and Ennedi mountains, precipitation occurs seasonally with rates up to 150 mm year–1. This precipitation could lead to diffuse recharge, as well as concentrated recharge along the episodically flooded wadis. Although it is clear that infiltration occurs under flooded areas, it is unknown if and to what extent the infiltration can recharge groundwater. This study combines remote sensing data on precipitation, evapotranspiration, and the temporal and spatial dynamics of the flooded areas with chemical and stable isotopic data from groundwater and surface water sampled between 2013 and 2016. The combination of these data shows that (1) the only area where diffuse recharge occurs is in the southern area of the Ennedi mountains, where concentrated recharge through the wadis occurs concurrently during the month of August, and (2) southeast of the Tibesti and north of the Ennedi mountains, only concentrated recharge occurs. The length of the flooded areas and thus the spatial extent of concentrated recharge varies significantly from year to year and can last up to 3 months. The study has shown that modern recharge does occur in northern Chad, but to a very limited extent, both in space and time. This means that achieving sustainable management of this renewable resource can only be considered through rigorous quantitative assessments. Furthermore, these findings have important implications for future studies on the regional dynamics of the NSAS.

Investigating the enigma of an irregular groundwater age pattern in a confined, presumed “fossil” complex aquifer through mixing cell flow modeling

Significant fluctuations in the groundwater (GW) age along the eastern flow path of the Nubian Sandstone Aquifer's (NSA), as derived from Krypton-81 groundwater dating, have suggested that this aquifer, located in Israel's Negev Desert and previously presumed to be a fossil, is not entirely isolated but mixes with younger and even recent water. The intermittent rejuvenation and drastic increases in the GW age across short distances most likely imply hydraulic connectivity with the surrounding aquifers, which contribute both younger and more ancient water to the NSA. The current study aims at modeling the GW flow system to locate and quantify its water sources despite the aquifer's hydrogeological complexity and the scarcity of hydrological data. We implemented the Mixing Cell Modeling (MCM) approach, understanding that the alternating rejuvenations and increases in the GW age downstream of the NSA's eastern flow trajectory reflect the mixing of the NSA's groundwater with young and old GW bodies, respectively. Thus, prompted by the 81Kr water age distribution, yet independent of the Kr radioisotope data, a multi-tracer mixing cell flow model was adopted based on a set of balance equations of water, dissolved minerals, and stable environmental isotopes. The findings indicate that (1) there is a small, yet substantial, intrusion of old brackish GW from a deep-seated, highly pressurized aquifer into the NSA in the northeastern Negev; (2) the rejuvenation of GW in the NSA is due to significant mixing with water from nearby overlying carbonate and chert aquifers, and (3) the NSA is substantially replenished through the Nubian Sandstone (NS) outcrops along the Negev Desert anticlines. Most GW intrusions into the NSA occur near the intersections of the eastern flow path with some of the Negev's major faults and synclines, such as the Paran and Ramon Fault zones and the Zin Syncline. In light of the relatively young GW age at the end of the NSA's western flow path in the northern Negev, and based on the similarities in the hydrogeological structures in the Negev and northern Sinai Deserts, we propose that similar mixing processes with GW from the overlying carbonate aquifers and direct GW recharge through the NS outcrops also occur in the northern Sinai Peninsula. The approach presented in this study might apply to examining recharge processes and hydraulic connectivity in other aquifers that were formerly classified as “fossil,” such as the immense NSA found in the Arabian (Jordan & Saudi Arabia) and the Western (Egypt) Deserts.

Investigation of groundwater based on stable isotopes and major ion geochemistry in the Eocene carbonate aquifer, East Beni-Suef area, Eastern Desert, Egypt

The East Beni-Suef region represents one of the most promising areas for agricultural development projects in Egypt. Groundwater from the Eocene Carbonate Aquifer is the main source of water for such projects all over the country. This aquifer covers about 50% of Egypt. It is shallower and easier to access with low drilling costs as compared to the Nubian Sandstone Deep Aquifer. This study aims to identify the origin and sources of recharge to this aquifer to better understand the sustainability and quality of the groundwater in this region. Stable isotopes and major ion geochemistry were used to achieve this goal. Groundwater samples and surface water from the Nile River were collected and analyzed for stable isotopes (δ18O and δD) as well as major ions such as Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, and SO42−. The results showed that groundwater samples varied in salinity from fresh to brackish (735 mg/L to 2680 mg/L). The major ion geochemistry revealed that the water type has evolved from Ca–Mg–HCO3 to Na–Cl–SO4. The suggested main processes that control the water chemistry in the study area are water-rock interactions involving evaporite dissolution and cation exchange. The results of δ18O and δD showed that the Eocene Carbonate Aquifer, in the study area, is mainly recharged from the Nile River and from the Nubian Sandstone Deep Aquifer at different ratios. The degree of contribution from these two end members was largely based on the location of wells from the Nile River, the water depth, and the structural setting. For the first time, depleted groundwater (δ18O = −10.16 ‰ and δD = −62.65 ‰) was recorded in the Eastern Desert, Egypt, in this research work. The assessment of groundwater quality for drinking and irrigation purposes is also provided in this study.

Assessment of the potential radiation hazards posed by Nubian sandstone, Egypt

The study found that the activity concentrations of the radionuclides 238U, 232Th and 40K in the sandstone are 32 ± 13, 29.6 ± 12.2, and 132.6 ± 86.4 Bq kg−1, respectively. These values are lower than the reported worldwide limits of 33, 45, and 412 Bq kg−1. According to the present study, the absorbed dose rate (Dair), the annual effective dose, and the excess life time cancer were all found to be below the worldwide mean. Pearson correlation, PCA, and HCA were used to analyze the data and identify patterns in the relationship between radionuclides and radiological hazards. A statistical analysis of the sandstones showed that the radioactive elements 238U, 232Th and 40K are the main contributors to the radioactive risk. The study suggests that the sandstone is safe to use. The levels of radioactivity are not high enough to pose a risk to human health.