Eocene Aquifer Research Articles

The effect of geology and agricultural development on the groundwater, West Minia, Egypt

Fifty groundwater samples were collected from the Oligocene sand and Middle Eocene limestone aquifers and analyzed for major ions and stable isotopes. Aquifer sediment samples were examined to determine hydraulic properties, and sixty-six well logs were investigated to understand the subsurface geology. The study reveals that lithofacies, mineral composition, and geologic structures significantly influence groundwater quality and behavior. Karst features in the Middle Eocene limestone aquifer create subsurface caves, leading to challenges such as abrupt salinization and well failure. In the Oligocene aquifer, groundwater is predominantly of the sodium chloride type. In the Middle Eocene aquifer, 80 % of samples are sodium chloride, with variations of sodium bicarbonate (10 %) and sodium sulfate (10 %) types. Remote sensing from 2013 to 2021 shows significant agricultural expansion, with vegetation increasing by over 227 km². This growth, driven by large agricultural projects, has led to substantial groundwater consumption, resulting in a 5-meter decline in water levels within just one year (from 2020 to 2021). The over-extraction poses a risk to the aquifers, threatening long-term sustainability. Understanding the region's geology is crucial for mitigating these issues and ensuring sustainable groundwater management.

Investigating the effects of surface water recharge on groundwater quality using hydrochemistry and ANFIS model: A case study Minia Governorate, Egypt

Monitoring and assessing groundwater quality and quantity lays the basis for sustainable management. Therefore, this research aims to investigate various factors that affect groundwater quality, emphasizing its distance to the primary source of recharge, the Nile River. To this end, two separate study areas have been considered, including the West and West-West of Minia, Egypt, located around 30 and 80 km from the Nile River. The chosen areas rely on the same aquifer as groundwater source (Eocene aquifer). Groundwater quality has been assessed in the two studied regions to investigate the difference in quality parameters due to the river's distance. The power of machine learning to associate different variables and generate beneficial relationships has been utilized to mitigate the cost consumed in chemical analysis and alleviate the calculation complexity. Two adaptive neuro-fuzzy inference system (ANFIS) models were developed to predict the water quality index (WQI) and the irrigation water quality index (IWQI) using EC and the distance to the river. The findings of the assessment of groundwater quality revealed that the groundwater in the west of Minia exhibits suitability for agricultural utilization and partially meets the criteria for potable drinking water. Conversely, the findings strongly recommend the implementation of treatment processes for groundwater sourced from the West-West of Minia before its usage for various purposes. These outcomes underscore the significant influence of surface water recharge on the overall quality of groundwater. Also, the results revealed the uncertainty of using sodium adsorption ratio (SAR), Sodium Percentage (Na%), and Permeability Index (PI) techniques in assessing groundwater for irrigation and recommended using IWQI. The developed ANFIS models depicted perfect accuracy during the training and validation stages, reporting a coefficient of correlation (R) equal to 0.97 and 0.99 in the case of WQI and 0.96 and 0.98 in the case of IWQI. The research findings could incentivize decision-makers to monitor, manage, and sustain groundwater.

Integrating MODFLOW and machine learning for detecting optimum groundwater abstraction considering sustainable drawdown and climate changes

Detecting optimum groundwater abstraction is a challenging objective. This study proposes a new approach for identifying the optimum pumping rates by integrating MODFLOW with machine learning (ML). The adopted strategy has been applied to the Oligocene and Eocene aquifers in the western desert of Minia, Egypt. MODFLOW-2005 model has been utilized to simulate various management scenarios, including current and expected climate scenarios of two Representative Concentration Pathways (RCPs): RCP 4.5 and RCP 8.5. The steady-state and transient MODFLOW models were calibrated using the groundwater levels of 37 observation wells with a coefficient of correlation (R2) of 0.986 and 0.988, respectively. The developed model has been run for 80 years, from 2020 to 2100. The results of MODFLOW demonstrated a drawdown in the groundwater level in the two aquifers, about 40, 41, and 42 m, owing to current climate conditions and scenarios of RCP 4.5 and RCP 8.5, respectively, in 2100. Generated data based on the calibrated model has been used to develop the ML models. ML models have been applied to predict the pumping rates using the well coordinates, aquifer type, evapotranspiration, the operating period in days, and drawdown as inputs. For this purpose, four ML models, Gaussian Process Regression (GPR), Support Vector Regression (SVR), Tree, and Artificial Neural Network (ANN)) were developed and evaluated. All ML models demonstrated an effective performance during the training and validation processes, particularly the GPR model, which has the best ability to predict the pumping rates with a correlation coefficient, RMSE, and Mean Absolute Error (MAE) equal to 1.0, 6.53, and 8.04, respectively. Therefore, the GPR model has been utilized to identify the optimum pumping rates. The findings of the GPR model revealed that the optimum abstraction of the Oligocene aquifer is 602266, 625329, and 635061 m3/day, while the Eocene aquifer’s optimal groundwater abstraction is 10229801, 1027906, and 102936 m3/day, considering the current climate, RCP 4.5, and RCP8.5, respectively. Anticipated findings are supposed to be instrumental for decision-makers, offering valuable insights into sustainable groundwater management. The novel integration methodology promotes the efficient use of groundwater, contributing to achieving sustainable development goals (SDGs).

Factors controlling lithium accumulation in brines from Upper Cretaceous to Lower Eocene aquifers of a continental evaporite basin

The origin of deep-seated Li-rich brines in a continental evaporite basin remains poorly understood. To clarify hydrogeochemical processes governing the Li enrichment, this study investigated chemical compositions and multi-isotopic (H–O–Li–Sr) features of a set of water samples from Upper Cretaceous to Lower Eocene sedimentary brines, saline groundwaters and oilfield brines, thermal waters and surficial river waters in the Jiangling Basin, central China. Waters from deep reservoirs evolve through multiple hydrogeochemical processes including evaporation, dilution, water-rock reactions and evaporite dissolution. These processes cause a range of Li and Sr contents (5.43–100 mg/L and 32.8–1307 mg/L) and isotope compositions (+8.6 to +19.3‰ and 0.706926–0.712480), indicating contributions from reservoir rock dissolution to δ7Li values and 87Sr/86Sr ratios. Chemical geothermometers applied to brines, saline waters and thermal waters give reservoir temperature values ranging between 70 and 200 °C. Temperature has a distinct effect on advancing host rock-water interactions, while high-temperature waters enhance leaching of Li in rocks compared to the low- and medium-temperature waters. The variable δ7Li values lower than river waters and high Cl/Br ratios in the Upper Cretaceous to Lower Eocene aquifers suggest a result of evaporite dissolution to different degrees, whilst waters in the Upper Cretaceous aquifers have the lowest δ7Li values similar to the thermal waters and the highest Cl/Br ratios suggest a stronger salt dissolution effect. Multi-isotope tracing highlights the role of temperature, reservoir rock types and different hydrogeochemical processes in defining the geochemical and isotopic water composition. Combination of these factors, together with high heat gradients associated with intense volcanic activity eventually results in Li accumulation in deep-seated brines from the Jiangling evaporite basin. Our results contribute to a further comprehensive understanding of hydrogeochemical processes that dominate deep brine formation and Li enrichment in an ancient continental evaporite basin.

ОСОБЛИВОСТІ ХІМІЧНОГО СКЛАДУ ПІДЗЕМНИХ ВОД У ТЕРИГЕННИХ ВІДКЛАДАХ ЕОЦЕНУ ТА АЛЬБ-СЕНОМАНУ В БАСЕЙНІ ДНІПРА

Background. The Dniprovsko-Donetskyi Artesian Basin is the largest hydrogeological region of the first order in Ukraine in both area and resources. The main forecasted resources within its boundaries are confined to the Eocene aquifer and the Alb-Cenomanian aquifer complex. These aquifer and complex are the principal ones - they are the basis for centralized water supply of a number of large settlements, so studying their chemical composition is of exceptional importance. The parts of the mentioned aquifer and complex that contain drinking water are identified as groundwater bodies (GWBs) – groundwater monitoring objects for which environmental objectives and risks of failure to achieve these objectives should be determined. At the same time, the natural water quality composition of these groundwater bodies groups is characterized by significant spatial heterogeneity, which should be taken into account when determining trends in its changes and specifying environmental objectives. The aim of the study was to establish the peculiarities of the spatial distribution of water with different chemical composition. The object of the study was aquifers in Eocene and Alb-Cenomanian sediments within the Dniprovsko-Donetsky artesian basin (Dnipro River Basin), and the subject was the chemical composition of water in these aquifers. Methods. To achieve these purposes, data on the chemical composition of the aquifer in the Eocene sediments and the aquifer complex in the Alb-Cenomanian sediments were collected, summarized and analyzed from published and fund sources. The information was processed using geographic information systems, and a database was created to generate specialized maps and perform joint data analysis. Results. In the article the mineralization and macrocomponent composition of groundwater in the terrigenous sediments of the Eocene and Albian-Cenomanian of the Dnipro basin are investigated and the peculiarities of their spatial distribution are established. Particular attention is paid to the areas where the exploitation reserves of both groundwater aquifers are explored. The qualitative, including microcomponent, composition of groundwater in terrigenous sediments of the Eocene and Albian-Cenomanian in Chernigiv City was characterized in detail. Peculiarities of formation of the chemical composition of groundwater in terrigenous sediments of the Eocene and Albian-Cenomanian were established. Сonclusions. It has been established that despite the fact that both GWBs are located in the zone of active water exchange, the content of macro- and microcomponents in them is quite different. In particular, in the water in the Alb-Cenomanian sediments, the macrocomponent composition of water is more homogeneous, and the content of macro- and microcomponents is characterized by a smaller range of variation. The identified peculiarities of the natural quality composition of the studied GWBs should be taken into account in the process of groundwater monitoring, in particular, when specifying environmental objectives and determining the frequency of groundwater quality state observations.

Hydrochemical and isotopic studies providing a new functional model for the coastal aquifers in Douala Coastal Sedimentary Basin (DCSB)/Cameroon

A new conceptual model of the hydrogeological systems in Cameroon's Douala Coastal Sedimentary Basin (DCSB) was constructed. The model is based upon the basin's known geology, plus data from recent field campaigns that allowed the collection of rainwater and groundwater samples for analyses of stable isotopes (δ2H, δ18O, δ13C), radiogenic isotopes (3H, 14C), and water chemistry. Aquifer characteristics that were thereby deciphered include recharge, isotopic distributions, residence times, and mixing processes. Rainfall samples (mean δ18O = −2.0 ‰; mean δ2H = −6.80 ‰; weighted mean = −2.4 ‰ δ18O, −9.85 ‰ δ2H) scatter along two distinct lines, thus indicating that local rainfall events undergo processes during convective events, variability in humidity, amount effects, and seasonal variations. Stable isotope values of river water samples are close to the weighted mean of local precipitation, with some downstream enrichment. The Quaternary/Mio-Pliocene superficial aquifer system (depth < 70 m) and the intermediate Oligocene/Upper Eocene aquifer system (depth: 70 to 200 m) exhibit evidence of similar fractionation processes through an enrichment gradient of δ-values. The enrichment is more pronounced at the top of the superficial aquifer, which is very exposed to direct rainfall water infiltration, evaporation, and amount effects. The depth profiles of δ-values coupled to water chemistry and tritium contents, evidence leakage between (i) the superficial system's Quaternary alluvium sands and Mio-Pliocene sands; and (ii) the superficial and intermediate systems. Thus, the aquifers that contain modern, post nuclear groundwater are characterized by flow exchanges and direct recharge from rainfall events. In contrast, the Upper Eocene system has depleted δ-values and lower bicarbonate contents, suggesting not only that this system was recharged by rapid infiltration (with limited effect of evaporation), but that this recharge occurred during a cooler time in the past. The residence times (computed from 14C dates) indicate uncorrected ages ranging from hundreds to thousands of years.

Vulnerability Study by DRASTIC Method for Eocene and Turonian Aquifers in the Tadla Plain

In numerous regions across Morocco, groundwater quality has undergone a significant decline in recent years, primarily due to factors such as agricultural expansion, improper solid waste disposal, and industrialization. This study presents an analysis of the vulnerability of two primary shallow aquifers, namely the Turonian and Eocene. The vulnerability assessment entails the evaluation of the aquifers' susceptibility to various forms of surface pollution, based on the physical characteristics of their surroundings. Within the Moroccan context, the DRASTIC method, integrated with Geographic Information Systems (GIS), emerges as the most suitable approach. This method involves the processing and analysis of seven factors pertaining to the three soil compartments, encompassing land cover, the unsaturated zone, and the saturated zone. Each chosen parameter is assigned a weight, reflecting its significance concerning groundwater protection. Notably, the water table's depth and the nature of the vadose zone exert the most substantial influence, followed by factors like recharge. Conversely, topography exhibits minimal impact, with soil type following suit. Lastly, the nature of the aquifer medium and its conductivity carry a moderate degree of influence. Each parameter is further categorized into classes, each defined by a specific rating. To derive an all-encompassing measure of vulnerability, the weights and scores of these various factors are synthesized through an additive model, yielding the comprehensive "DRASTIC Index." Subsequently, this index is employed to assess the intrinsic vulnerability level of the Turonian and Eocene aquifers by superimposing the seven index maps.

Applying Geophysical and Hydrogeochemical Methods to Evaluate Groundwater Potential and Quality in Middle Egypt

The El-Minia district is a location of interest for future urban development. Using hydrochemistry and electrical resistivity studies, this work aimed to evaluate the groundwater potentiality and it’s suitable for various uses. The groundwater potential in the study area was evaluated based on 24 VESs (vertical electrical soundings), and its quality was determined based on the analyses of 57 groundwater samples. EC (salinity index), Na% (salt hazard), SAR (ratio of sodium adsorption), chloride risks, SSP (soluble sodium percentage), MH (magnesium hazard), and other indicators were used to determine whether the collected water samples were suitable for irrigation. Four layers in the study area are mentioned in the geoelectrical cross-sections that have been constructed. The first is made up of silt and clay from the Nile River, while the second is made up of sandy clay, which has a resistivity range of 15 to 32 Ohm.m and a range thickness of 2 to 68 m. Dry limestone makes up the third layer; its resistivity ranges from 1222 to 3000 Ohm.m and its thickness varies between 75 and 95 m. The Eocene aquifer in the research area is represented by the final layer, which has a thickness of more than 250 m and resistivity values that range from 602 to 860 Ohm.m. Most groundwater samples that were collected are safe for drinking; however, none of them are fit for home usage because of their extreme hardness. According to the SAR and US diagram, RSC, KR, and PI, most groundwater samples from the Pleistocene and Eocene aquifers are fit for irrigation.

Planning for groundwater management using visual MODFLOW model and multi-criteria decision analysis, West–West Minya, Egypt

This study presents a planning model to assist decision-makers in implementing proposed sustainable development policies based on the government's development schemes. It focuses on the exploitation of groundwater from the Eocene aquifer in the West–West Minya region in the Western Desert of Egypt as one of the new development areas. The visual MODFLOW model is applied to serve as a base model for the study area's local modeling and assess the impact of operating scenarios on the groundwater aquifer. An optimal scenario for groundwater sustainability is achieved by considering the water meter consumption in the newly reclaimed area with a value of 6 m3/d for each acre to irrigate 3953.68 acres; the maximum drawdown of about 60 m is formed after 9700 days of simulation. The GIS multi-criteria analysis model is used to assess the impact of groundwater deficiency as a result of reclamation. Results of the groundwater model are merged as input layers in multi-criteria decision analysis, which include groundwater salinity, groundwater levels, aquifer transmissivity, and aquifer storativity. The prospective groundwater zones are categorized into most suitable (1584 km2, 9.9%), suitable (4592 km2, 28.7%), good (4784 km2, 29.9%), moderate (1488 km2, 9.3%), and unsuitable (3552 km2, 22.2%). It is recommended to optimize levels of groundwater withdrawal from the current or future drilling wells to achieve a balance between the use and the protection of water potential.

Decision Support System for Sustainable Exploitation of the Eocene Aquifer in the West Bank, Palestine

Groundwater is a crucial resource for water supply and irrigation in many parts of the world, especially in the Middle East. The Eocene aquifer, located in the northern part of the West Bank, Palestine, is threatened by unsustainable groundwater abstractions and on-ground pollution. Analysis and management of this aquifer are challenging because of limited data availability. This research contributes to the long-term sustainability of the aquifer by model-based design of future abstraction strategies considered within an uncertainty analysis framework. The methodology employed started with development of a single-layer steady-state MODFLOW groundwater model of the area, followed by uncertainty analysis of model parameters using Monte Carlo simulations. The same model was afterwards coupled with a Successive Linear Programming (SLP) optimization algorithm, implemented in the Groundwater Management tool (GWM) of the United States Geological Survey (USGS). The purpose of optimization was deriving five optimal abstraction strategies, each aiming to maximize groundwater abstraction, subject to different constraints regarding groundwater depletion. Given the uncertainty of model parameters, the sensitivity and reliability of these optimal strategies were then tested. Sensitivity was checked for two optimal strategies by performing re-optimization with different values of uncertain model parameters (one at a time). Reliability of the five strategies was tested by analyzing the extent of constraints’ violation for each strategy when varying the uncertain parameters using Monte Carlo simulations. Finally, the model was used for determining capture zones of wells for the five optimal abstraction strategies, land-use in these capture zones, and the associated estimates of on-ground nitrogen loading. The developed strategies were then deployed in a web-based decision support application (named Groundwater Decision Support System—GDSS), together with other relevant information. Users can analyze results of different optimal strategies in terms of groundwater level variations and total water balance results, and test consequences of uncertain parameters. Capture zones of wells for different abstraction strategies, together with land-use and on-ground nitrogen loading in these capture zones, are also presented. Results show that critical uncertain parameters are recharge, hydraulic conductivity, and conductance at key boundary condition locations. Optimal abstraction strategies results indicate that an increase in total abstractions could be between 5% and 20% from the current level (estimated at about 56 × 106 m3/year, which is about 74% of estimated annual recharge). The uncertain parameters, however, are impacting the sensitivity and the reliability of the optimal strategies to variable degrees. Recharge and hydraulic conductivity are the most critical uncertain parameters regarding sensitivity of the optimal strategies, while reliability is also impacted by the level of abstraction proposed in a given strategy (number, locations, and abstraction rates of new wells). The main novelty and contribution of this research is in combining modelling, uncertainty analysis, and optimization techniques in a comprehensive decision support system for the area of the Eocene aquifer, characterized with limited data availability.

Isotopic, Geophysical, and Hydrogeochemical Investigations of Groundwater in West Middle Upper Egypt.

The groundwater of the west Assiut and El-Minia districts was evaluated in this paper using geoelectrical, hydrogeochemical, and stable isotope (oxygen-18 and deuterium) studies. In the studied localities, 42 vertical electrical soundings (VES) were taken to evaluate groundwater potential, and the analysis, as well as collection, of 74 samples of Eocene groundwater was carried out. In accordance with the vertical electrical soundings' interpretation, there are four geoelectrical formations and two major water-bearing units that act as aquifers (Pleistocene and Eocene). To determine irrigation suitability, the sodium absorption ratio (SAR), electrical conductivity (EC), residual sodium carbonate (RSC), sodium percentage (Na %), magnesium hazard (MH), Kelley's ratio (KR), and permeability index (PI) were evaluated as irrigation quality parameters. The EC, Na %, and the diagram of the US salinity laboratory indicated that most of the collected samples of groundwater were suitable for irrigation, whereas the RSC and PI pointed out that all of the collected water samples were safe for irrigation. The oxygen and hydrogen isotope values in groundwater samples showed that the Eocene aquifer was recharged by both surface water and the Nubian aquifer.

Identification of Groundwater Bearing Zones Using Geoelectrical and Electromagnetic Techniques at Tourah Area, South of Cairo - Egypt

The complex geology of Tourah area, south Cairo is a serious challenge for groundwater exploration, where the risk of unsuccessful groundwater drilling excavation for industrial purposes is well dressed, raising the need for better geophysical subsurface detection and characterization approaches in terms of water bearing and aquitard zones. Datasets from the study area were acquired using integrated geophysical techniques comprising of one Dimensional Vertical Electrical Soundings (1D VES) and one Dimensional Transient Electromagnetic (1D TEM) as well as two-Dimensional Electrical Imaging (2D ERI) which was restricted to the available spreading space as well as subsurface infrastructure noise. The results of 1D VES and 1D TEM soundings detected three to five geoelectric layers used to generate geoelectrical cross sections and maps of resistivity, thickness, and depth to water bearing zone. Moreover, the 2D ERI inversion profiles were able to image the first three layers and the depth of the water bearing zone [A] with significantly greater resolution due to their higher lateral and vertical resolutions compared to the traditional 1D VES and TEM interpolated cross section. The integration of the three geophysical methods displayed a smooth distribution of both marly limestone and fractured shaly limestone and claystone bands water bearing zones [A and B]. Resistivity values of the water bearing zone [A] ranges from 0.1 to 24 Ω m, with average thickness of 4 to 12 m, and depth to water of 1.5 to 13.6 m. In addition, [zone B] is the main water bearing zone of fractured shaly limestone and claystone bands (2 to 14 Ω m) which is detected at deep depth of 40 and 75 m. Two normal fault systems inferred from 1D interpretation are considered responsible for local recharging of the main Eocene aquifer over the study area. In conclusion, the outlined water bearing thickness as well as limited sources of groundwater recharge indicate that these water bearing zones may not provide a sustainable supply for the industrial development purposes in the future.

Hydrogeochemical assessment of the Carbonate rocks of the Eocene aquifer in the eastern Nile valley, Egypt

The goal of the ongoing research is to better understand the physical-chemical mechanisms that regulate the physical and chemical characteristics of groundwater resources in the studied region. The water samples were obtained at different depths varied from 120 m to 230 m. The physicochemical properties of fourty groundwater points were obtained through the fractured limestone aquifer, such as Na

Integration of hydrochemical and isotopic characteristics for identifying groundwater recharge sources of the Eocene carbonate aquifer, Western Desert, Egypt

The Western Desert is considered as one of the most promising areas for groundwater resource and development in Egypt. The Eocene carbonate aquifer is one of the most exploited aquifers for development in the Egyptian Western Desert, especially in the area west of El-Minia in central Egypt. The present study aims to assess the hydrochemistry of the Eocene carbonate aquifer and the possible recharge sources to this aquifer in the western desert west of El-Minia district. Fifteen groundwater samples from the Eocene carbonate aquifer were analyzed for major ions, heavy metals, oxygen-18, and deuterium to assess the hydrochemistry and isotopic compositions in this area. TDS concentrations ranged from 510 to 1408 mg/l. However, the cluster analysis of the Eocene groundwater samples in the present work, reveals two main groups (A and B) with different chemical and isotopic characteristics. The chemical composition of the studied samples showed that the main chemical facies are Na–Cl, Na–Ca–HCO3, and Na–Cl–HCO3. Silicate weathering control the majority of groundwater samples of the Eocene aquifer, while carbonate dissolution governing the deep groundwater of Eocene carbonate aquifer. Isotope ratios of oxygen (18O) and hydrogen (2H) were used to identify the recharge sources, which showed relatively depleted 18O and 2H isotopic ratios and relative mixing of groundwater from the Eocene Limestone with paleowaters from the deep Nubian aquifer and water from the Nile River. However, the mixing ratio depends mainly on the distance from the Nile River, depth to groundwater, and local geologic structures also contribute to the mixing pattern. The present study indicates the need for a detailed structural study to detect the locations and properties of fractures as it plays a vital role in feeding the Eocene aquifer from the underlying aquifer. Integration of hydrogeochemical data and isotopic compositions provide a better understanding of the geochemical processes that control the groundwater hydrochemistry of the Eocene carbonate aquifer west of El-Minia, Egypt and in areas with similar conditions.

Hydrochemical characteristics and quality assessment of groundwater aquifers northwest of Assiut district, Egypt

Groundwater quality assessment is essential for the sustainable development of groundwater resources and for determining their use for domestic, irrigation, or industrial purposes. The objective of this study is to determine the hydrochemical characteristics and water quality of the groundwater aquifers in the area to the northwest of Assiut district, Egypt, and to map their spatial variations in terms of suitability for domestic and irrigation purposes. Two main aquifers are presented in the study area, the Pleistocene and the Eocene aquifers. Water samples were collected from 58 wells across the study area and analyzed to determine their physicochemical properties and calculate the water quality indices. The hydrochemical investigation shows that the domination of the major ions in the Pleistocene aquifer is in the following order: Na+ > Ca2+ > Mg2+ > K+ and Cl− > HCO−3 >SO−4 but it takes the trend of Na+ > Mg2+ > Ca2+ > K+ and Cl− > HCO−3 >SO−4 in the Eocene aquifer. Most of the Pleistocene aquifer samples are suitable for drinking while about a half of the Eocene samples are unsuitable for drinking due to their high salinity that ranges from 235 to 2830 for the former and from 350 to 4150 for the latter. The Eocene water samples and most of the Pleistocene water samples are unsuitable for domestic use due to the high level of hardness that ranges from 67.88 to 1923 for the former and from 26.56 to 944.6 for the latter. Groundwater suitability for irrigation was assessed based on sodium adsorption ratio (SAR), residual sodium carbonate (RSC), Kelley ratio (KR), the magnesium hazard (MH), and potential salinity (PS). Most of the Pleistocene and a half of the Eocene samples are suitable for irrigation. Maps showing the spatial variations of different groundwater quality parameters were produced using ArcGIS.

Joint Gravity and Seismic Reflection Methods to Characterize the Deep Aquifers in Arid Ain El Beidha Plain (Central Tunisia, North Africa)

Electric resistivity sounding and tomography, as well as electromagnetic sounding, are the classical methods frequently used for hydrogeological studies. In this work, we propose the development and implementation of an original integrated approach using the unconventional hydro–geophysical methods of gravity and seismic reflection for the fast, large–scale characterization of hydrogeological potential using the Ain El Beidha plain (central Tunisia) as an analogue. Extending the values of vintage petroleum seismic reflection profiles and gravity data, in conjunction with available geological and hydrogeological information, we performed an advanced analysis to characterize the geometry of deep tertiary (Oligocene and Eocene) aquifers in this arid area. Residual and tilt angle gravity maps revealed that most gravity anomalies have a short wavelength. The study area was mainly composed of three major areas: the Oued Ben Zitoun and Ain El Beidha basins, which are both related to negative gravity trends corresponding to low–density subsiding depocenters. These basins are separated by an important NE–SW trend called “El Gonna–J. El Mguataa–Kroumet Zemla” gravity high. Evaluation of the superposition of detected lineaments and Euler deconvolution solutions’ maps showed several NE–SW and N–S relay system faults. The 3D density inversion model using a lateral and vertical cutting plane suggested the presence of two different tectonic styles (thin VS thick). Results from the gravity analysis were in concordance with the seismic analysis. The deep Oligocene and Eocene seismic horizons were calibrated to the hydraulic wells and surrounding outcrops. Oligocene and Eocene geological reservoirs appear very fractured and compartmented. The faulting network also plays an important role in enhancing groundwater recharge process of the Oligocene and Eocene aquifers. Finally, generated isochron maps provided an excellent opportunity to develop future comprehensive exploration surveys over smaller and more favorable areas’ sub–basins.

Mapping of groundwater opportunities for multi-purposes use in Beni-Suef province, Egypt

Beni-Suef desert represents one of the interesting areas for land reclamation and future urban areas. This work aimed to assess the groundwater potentiality and suitability for different purposes by using the electrical resistivity and hydrochemistry studies. In the area of investigation, 32 vertical electrical soundings (VES) were implemented in order to determine the groundwater potentiality, as well as 42 samples of water were collected and analyzed. The suitability of gathered samples of water for irrigation was evaluated throughout: salinity index, sodium hazard (Na %), ratio of sodium adsorption (SAR), chloride hazards, soluble sodium percentage (SSP), magnesium ratio (MH), and other indicators. Results were represented in “Opportunity Map” by GIS layers, to denote major element distribution. Analysis indicated a presence of two potentiality zones in the study area that refer to Quaternary and Eocene aquifer. Results indicated that the east and north parts of the area of investigation have low groundwater potentiality for irrigation and domestic uses, whereas southern region has medium groundwater potentiality. On the other hand, all the gathered samples of groundwater are inappropriate for domestic use. Most of the studied groundwater samples can be used for irrigation according to SAR and US salinity chart, residual sodium carbonate (RSC), Kelly’s ratio (KR), and permeability index. The prepared opportunity map reflects the evaluation of water potentiality in the study area.

Characterization and sampling of a deep and heterogeneous aquifer – An application to the Paleocene – Eocene aquifer in the Aquitaine basin, France

Groundwater sampling in boreholes has been carried out for decades according to well-established protocols and regulations. An important requirement in this context is the need to purge the borehole prior to any sampling action, the volume of the purge being adapted to the water flow and the regulatory context. Contaminated site investigations have introduced the concept of water column heterogeneity in the screened section of boreholes, which also occurs in some uncontaminated boreholes or in long-screened boreholes. Specific guidelines and practices were thus introduced, in particular the concept of discrete sampling. This type of sampling can be advantageously used in deep boreholes, provided that there is some renewal of water at the screens or the perforated intervals. The present study aims to take a step forward in the characterization of deep boreholes set up in the Aquitaine basin in France, by defining a protocol for relatively short boreholes (depth < 170 m) and applying it to much deeper boreholes, formerly drilled for oil and gas exploration (sampling up to 1035 m deep). Acquisitions were performed to better characterize water chemistry, including some isotope considerations. They were based on physico-chemical logging and endoscopic inspections where technically possible. After a review of the information provided by the investigations on the characterization of the Paleocene – Eocene aquifer in southwestern France, a methodology is proposed to make sampling in deep boreholes with low-yield more reliable, by combining the abstraction of a reduced water volume and the use of a downhole sampling system.

Ferruginous accumulations in hypogene karst conduits of Crimean Piedmont: Evidence for a deep iron source for the Kerch-Taman iron-ore province, north Black Sea region

This study documents ferruginous accumulations in hypogene karst cavities in the Eocene limestones of central-eastern Crimean Piedmont, including unusual quartz-goethite tubes in Tavrida Cave, and aims to reveal their origin and significance to the problem of iron source for the adjacent Kerch-Taman iron ore province. We employed speleological, petrographic, mineralogical, and geochemical (including REE analysis) methods. Ferruginous materials dominated by goethite precipitated in open cavities, although metasomatic replacement of the host rock also occurred. Although the formation of conduits/cavities enclosing ferruginous materials clearly predated the main phase of hypogene speleogenesis in Tavrida Cave, both speleogenetic phases were controlled by the same cross-formational flow paths. Geochemical characteristics of the studied materials in all sites are largely similar, pointing to their genetic affinity. REEY patterns in most of the samples are remarkably similar to those found in iron formations worldwide, for which significant hydrothermal contribution is established. We show that these accumulations had been formed from acidic, reduced, hydrothermal fluids rising from a deep source and intruding oxidizing environment of the karstified Eocene aquifer, where goethite had been precipitated at the boundary of the iron reduction/oxidation zone. This mechanism is consistent with the hypogene origin of host karst conduits. These findings have implications to the origin of iron ores in the adjacent Kerch-Taman province, where deposits are closely associated with mud volcanoes operating there since at least the Middle Miocene. Although the marine sedimentary (hydrogenetic) origin of these deposits is universally accepted, the source of iron is a matter of debate. Revealing of the deep fluid source of iron for the ferruginous accumulations in hypogene caves in Piedmont suggests that the deep fluid system associated with mud volcanism in the Kerch-Taman region could have been a significant, if not the major, supplier of iron for ore deposits in the Cimmerian basin.

Stratigraphic architecture and depositional environment of the Paleocene-Lower Eocene aquifers system (Douala onshore basin, SW Cameroon)

The Paleocene-Lower Eocene N'kapa Formation has long been considered as an important groundwater and hydrocarbon resource in the eastern edge of the Douala Basin. The present study’s aim is to establish a possible link between the geological nature of this formation and the quality of potential aquifers using Gamma Ray well log, cuttings and outcrops through sedimentology and sequence stratigraphy studies. The results obtained from this study show that: lithofacies are dominated by clays, silts and sands/sandstones; gamma ray electrofacies are funnel-shaped to cylindrical-shaped with some bell-shaped; depositional environments are continental to shallow marine dominated by fluvial and sometimes tidal processes; fluvial channel-fill, tidal channel-fill and delta front bars sands are potential aquifers; sequence stratigraphy analysis reveals two transgressive–regressive cycles of second order (Danian to Selandian and Thanetian to Ypresian), two Highstand System Tracts, one Transgressive System Tract and one Lowstand System Tract; the high-resolution geometry of these sandy/sandstone sedimentary bodies shows that their distribution is linked to the hydrodynamic factors and the topography of the depositional environment. A total of two types of lithological facies of the reservoir levels were defined according to the volume of clay: clean sandstone (0–15%) and low clayey sandstone (15–30%). The gamma ray well log correlation shows that the thickness of the reservoir levels is variable and that the clay content (Vsh%) increases from the NE to the SW. As a result, the best potential aquifers appear to correspond to the fluvial channel-fill sands deposited during the base-level fall of Upper Paleocene age (Lower Thanetian).