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Southern Tunisia belongs to the Sahara desert, one of the driest regions of the world, where groundwater research is crucial to satisfy the water demand. In this region, the Jurassic aquifer appears as a potential resource. Nevertheless, the related information is too limited to develop a suitable plan for exploitation. The present study aimed for a thorough understanding of the Jurassic series using borehole and seismic reflection data. Well logs from 40 petroleum boreholes were analyzed both qualitatively and quantitatively to define precisely the potential water reservoirs and determine their petrophysical characteristics. Comparison of the various recordings revealed the abundance of sandstone and dolomite deposits in the Sebaia Formation (Dogger–Malm) and the evaporitic composition of the Abreghs Formation (Lias). The Sebaia Formation is enriched in clays toward the south as indicated by well logs correlation and computed shale volumes (Vsh reaching 27.8%). The south-east part of Southern Tunisia contains mostly sandy Jurassic reservoirs, exhibiting the highest estimated porosities (22.8–31%). Lithostratigraphic correlations were established to firstly approach the geometry of the Jurassic aquifer. These correlations highlighted that the Jurassic series have variable depth and thickness along the Dahar structure, which thicken and deepen from the Dahar to the west and disappear in the Jeffara. These findings were further refined by the interpretation of 198 seismic profiles, which display several NW–SE-, E–W- and NE–SW-trending normal faults that influenced the Jurassic reservoirs depth, thickness, facies and petrophysical characteristics as well as groundwater circulation. The present study yielded interesting results that may enormously guide the investigation of the Jurassic aquifer in Southern Tunisia. Furthermore, it may be considered as an example for hydrogeophysical applications in the "Sahara" and other arid zones worldwide. [ABSTRACT FROM AUTHOR]

This research paper presents an investigation of an aquifer structure using a combination of gravity and seismic analyses, calibrated by hydrogeological data. This work illustrates how crucial it is to study geological structures and fault networks as preliminary work to understand water- and pollutant-flow systems and aquifer vulnerability, especially with the increased frequency of drought events and climate change pressures. A Plio-Quaternary coastal northeastern aquifer in Tunisia was chosen as the study case. First, a hydrogeological approach was performed using water wells, and piezometer data showed an important fluctuation in the piezometric level and a notable depression in the piezometric surface observed in the southern part of the study area. Secondly, gravity data were analysed and calibrated using a seismic profile. The results demonstrated the presence of shallow NE–SW faults less than 300 m below the region's principal wadis, as well as deeper faults of varying depths (from 400 to 2600 m) that influence the basin structure, aquifer geometry and resulting water flow. The combination of these approaches revealed that the variations in the aquifer thickness, piezometric surface depression zones and groundwater flow are mainly controlled by shallow and deep geological structures and their tectonic reactivation. [ABSTRACT FROM AUTHOR]

The objective of this study is to contribute to identify the hydrogeochemical and isotopic characteristics and groundwater quality aptitude for irrigation and drinking water uses in arid and semi-arid areas. The study area is the Djeffara of Medenine, in southeastern Tunisia. This region is facing increasing drinking water needs due to a rapidly growing population, increased urbanization and touristic activities. Fresh groundwater is the main source of water supply. The methodology used a hydrogeological survey as well as periodic sampling campaigns and interpretation of geochemical and isotopic groundwater data in the study area. Results demonstrated that the mineralization increase from upstream to downstream and its origins is the dissolution of sulphated salts (gypsum, anhydrite, epsomite, burkeite, thenardite and mirabilite) and chloride (halite and magnesium chloride) associated with the crust. Results approve hydrogeological communication between Zeuss Koutine (ZK) and Sahel El Ababsa Triassic sandstone (TSE) aquifers and the rainwater direct recharge of the two aquifers of the Djeffara groundwater system. Furthermore, the groundwater quality map shows three water types: suitable, moderate and unsuitable water for irrigation purposes. While, results for drinking purposes demonstrate that the ZK aquifer is more favorable for drinking than Triassic SE aquifer. Which 86 percent of resources really used for drinking water by the National Company of Drinking Water Supply (SONEDE) and rural water supply by regional Commissary for Agricultural Development (CRDA) [24]. [ABSTRACT FROM AUTHOR]

The Nefza aquifer system in northern Tunisia has long been used for drinking water in its southern part. The decline in groundwater levels since the 1980s in the exploited area has prompted water management to concentrate on the depletion of the groundwater resource, despite limited understanding of the overall availability of the aquifer system. The objective of the current paper is to determine the amount of groundwater stored in the aquifer system, which has never been accurately assessed until now. The methodology involves the creation of a comprehensive database utilizing all available lithological and geophysical information, designing a 3D model of the aquifer system, and incorporating hydrodynamic parameters to estimate the groundwater storage. The model shows the spatial distribution of groundwater storage and enhances the mapping of the aquifer's geometry, as well as distinguishes the key aquifers and aquitards. Over 45 km2 of the modeled area, the calculated groundwater storage in 2019 was around 3 × 109 m3 with a highly variable spatial distribution. It was found that the area currently exploited for drinking water supply represents a poor groundwater storage range between 97 and 377 m3/voxel (voxel dimension = 1000 m × 1000 m × 5 m), while the non-exploited area had an excellent groundwater storage that can reach 798 m3/voxel. In addition, over the last 52 years (1976–2019), only 0.2% of the amount of groundwater stored in the aquifer has been depleted. The study suggests that water management should focus on accessing the non-exploited areas, even though the cost of development may be high. Further research into groundwater flow in the region is needed through multiple methods, such as geochemistry and hydrodynamic modeling. [ABSTRACT FROM AUTHOR]

The North-Western Sahara Aquifer System (NWSAS) is a complex multi-layered aquifer system with extraordinary continental groundwater reserves. This largest aquifer in the world straddles three countries: Algeria, Libya, and Tunisia. It contains more than 50,000 billion cubic meters of water; of which 70% is in Algerian territory in the southeast of the country. This water is the result of accumulation over 1 million years. In the Wadi Mya basin (Algeria), this system is characterized by two overlaid aquifer systems: the complex terminal (CT), a shallow aquifer housed in the Senonian-Eocene and Mio-Pliocene formations, and the continental intercalary (CI), a deep aquifer hosted in the Albian, Aptian and Barremian formations. The main purpose of this study is to carry out a correlation between the geochemical composition of the water and the facies of the aquifer formation. The adopted approach will allow deciphering the hydro-chemical relationships between the different levels of the two aquifer systems in the Wadi Mya basin. To acquire the chemical composition of water, the study method goes through a targeted sampling and physicochemical analysis of water followed by a statistical analysis as well as correlation and geochemical modelling: the interpretation of specific diagrams (Piper), correlations between chemical elements in binary graphs, and principal component analysis (PCA). The performed geochemical modelling by examining the saturation index and chemical balance of water helps to better understand the origin of mineralization, elucidate the mixing of waters originating from different aquifers, as well as highlight the relationship between deep and shallow aquifers in the Wadi Mya Basin hydrodynamic conversion. The obtained results indicate that the overall mineralization occurring within the study area is dominated by sodium chloride and calcium chloride-sulfate facies. This can be explained by the dissolution of halite, gypsum, and anhydrite evaporitic rocks, intercalated in the aquifer matrix besides the effects of the extended stay of fossil waters with low recharging and cation exchange reactions resulting from water-rock interactions. The interference recorded between the geochemical signatures of the two aquifers favors the hypothesis of interconnection between aquifers through fractures. Through the implementation of such academic research, this invaluable source of life will stay sustainable for future generations. [ABSTRACT FROM AUTHOR]

Groundwater resources are increasingly under demand to support human activities and economic development. This naturally clean resource is threatened by human and natural pollutions. Protecting groundwater has become a challenge for both urban and rural communities. This work aims to develop a simple and effective approach to assess the risk of aquifer pollution and the delineation of risk zones. To do so, an aquifer risk index (ARI) was presented as an overall indicator of the risk of groundwater pollution. The ARI is calculated using the groundwater vulnerability index (GVI) and the normalized water quality index (WQI). The multi-linear regression (MLR) model was used to assign weights to each parameter. This model has been applied and validated in the Koutine area of southern Tunisia. The results revealed that the groundwater in the study area is characterized by low and moderate risk. Fifty-six percent (56%) of the total study area presents a low risk. The remaining 44% of the study area is classified as medium risk, primarily in the Wadi and Lowland plains. ARI considers the intrinsic characteristics of the aquifer and groundwater quality when assessing the risk of pollution. The approach developed for assessing groundwater risks is simple to implement, realistic, and efficient. AVI is a parametric approach that uses aquifer data without losing information. This method can assist academics and groundwater resource managers in delineating risk areas to protect groundwater resources from pollution. [ABSTRACT FROM AUTHOR]

The Mateur multi-aquifer system, consisting of a Quaternary alluvial aquifer and a Campanian limestone aquifer, is one of the most significant aquifer systems in northern Tunisia, providing domestic and agricultural water supply for the entire Mateur region. The present study aims to unveil the various factors and mechanisms controlling the groundwater chemistry of such a system. Indeed, integrated hydrogeochemical and isotopic approaches are used herein to identify the alluvial and limestone aquifer waters mixing and evolution in the Mateur region. Results show that despite the difference in aquifer lithology, there is little difference in the major ion geochemistry and stable isotope ratios of groundwater within the Mateur plain. Waters from the Quaternary alluvial aquifer are classified into two predominant facies: mixed facies (Ca–Na–SO4–Cl and Ca–Na–HCO3–Cl) and Na–Cl facies. Similarly, waters from the limestone aquifer have also mixed facies (Ca–Na–SO4–Cl) and sodium chloride facies (NaCl). Groundwater δ18O and δ²H values show more homogeneous values along the groundwater flow direction, indicating inter-aquifer mixing processes. Tritium contents of the Campanian aquifer are lower than those of the Quaternary aquifer, indicating a relatively older age or mixture with recent waters. This validates a concept of the hydraulic continuity between the Quaternary aquifer and the Campanian aquifer which is consistent with the geochemical analytical results. [ABSTRACT FROM AUTHOR]

The aquifer system of Menzel Bourguiba, located in northeastern Tunisia, is an important groundwater resource that, for the last decades, has been a subject of excessive use by agricultural and industrial activities leading to the degradation of its water quality. To better understand the hydrochemistry of these aquifers, identify the main factors controlling their mineralization, and assess their suitability for drinking and agricultural purposes, 35 groundwater samples collected during the campaign of October 2019 were analyzed by different physicochemical methods. The results showed that the hydrochemical facies of the study area is characterized by two major types SO4-Cl-Ca and Na–Cl. The total dissolved solids (TDS) values range from 0.5 to 1.9 g/L in the shallow aquifer and from 0.6 to 2 g/L in the deep aquifer. The high rates are recognized downstream of the studied basin. The interpretation of multivariate statistical analysis and geochemical approaches revealed that rock-water interaction, dissolution and precipitation process, ionic exchange mechanisms, water irrigation return, and marine intrusion are the main factors controlling the mineralization of the study area groundwater. The comparison of the analytical data to the Tunisian and World Health Organization (WHO) standards unveiled that the majority of groundwater samples are unsuitable for drinking because of high nitrate contents, elevated electrical conductivity (EC), TDS values, and high concentrations of some chemical parameters. In addition, the sodium absorption ratio and the sodium percent parameters indicated that most of the analyzed samples are inappropriate for irrigation uses. [ABSTRACT FROM AUTHOR]

Like most North African countries, Tunisia is characterized by a harsh arid and semi-arid climate with scarce water resources and poor water quality on most of its territory. The quality of groundwater is not immune to pollution. Sminja aquifer, located in Zaghouan district in Northeastern Tunisia, has been used to meet Zaghouan agglomeration needs for drinking purposes and irrigation uses. On the other hand, the region has suffered from inefficient usage and mismanagement of water resource due to appropriate legal, political, and economic frameworks to take into consideration the regional vulnerability to climate change and population growth. The application of the Susceptibility Index (SI) makes it possible to evaluate the impact of agricultural activities on the water quality in Sminja aquifer, using five parameters [depth of water (D), net recharge (R), aquifer media (A), topography (T) and Land use (LU)]. Modular three-dimensional multispecies transport model was used to assess, simulate and predict pollution transport of nitrate. The vulnerability index's spatial distribution shows that the most vulnerable area was found in the extreme north of the Sminja aquifer. It shows that a high vulnerability characterizes 21% of the study area (70 < SI < 60). The moderate to high vulnerability areas to pollution occupied 12% of the aquifer and the moderate to low vulnerability zones occupied 67% of the total area. The outputs of the SI reflect a good correlation with the measured nitrate concentrations. After calibration completion, the MT3DMS transport model results showed a good correlation between measured and simulated nitrate concentrations. The predict scenarios show that the nitrate propagates in all the aquifer, from the irrigated area to the non-irrigated area. [ABSTRACT FROM AUTHOR]

The study of water quality and the quantification of reserves and their variations according to natural and anthropogenic forcing is necessary to establish an adequate management plan for groundwater resources. For this purpose, a modeling approach is a useful tool that allows, after calibration phase and verification of simulation, and under different scenarios of forcing and operational changes, to estimate and control the groundwater quantity and quality. The main objective of this study is to collect all available data in a model that simulates the Jeffara of Medenine coastal aquifer system functioning. To achieve this goal, a conceptual model was constructed based on previous studies and hydrogeological investigations. The regional groundwater numerical flow model for the Jeffara aquifer was developed using MODFLOW working under steady‐state and transient conditions. Groundwater elevations measured from the piezometric wells distributed throughout the study area in 1973 were selected as the target water levels for steady state (head) model calibration. A transient simulation was undertaken for the 42 years from 1973 to 2015. The historical transient model calibration was satisfactory, consistent with the continuous piezometric decline in response to the increase in groundwater abstraction. The developed numerical model was used to study the system's behavior over the next 35 years under various constraints. Two scenarios for potential groundwater extraction for the period 2015–2050 are presented. The predictive simulations show the effect of the increase of the exploitation on the piezometric levels. To study the phenomenon of salinization, which is one of the most severe and widespread groundwater contamination problems, especially in coastal regions, a solute transport model has been constructed by using MT3DMS software coupled with the groundwater flow model. The best calibration results are obtained when the connection with the overlying superficial aquifer is considered suggesting that groundwater contamination originates from this aquifer. Recommendations for water resource managersThe results of this study show that Groundwater resources of Jeffara of Medenine coastal aquifer in Tunisia are under immense pressure from multiple stresses.The water resources manager must consider the impact of economic and demographic development in groundwater management to avoid the intrusion of saline water.The results obtained presented some reference information that can serve as a basis for water resources planning.The model runs to provide information that managers can use to regulate and adequately control the Jeffara of Medenine water resources. [ABSTRACT FROM AUTHOR]

Monitoring the groundwater quality situation and identifying the various pollution loads' sources are a prerequisites to finding solutions. In many areas, nitrate and salinity are one of the prime pollutants in the groundwater. This investigation is carried to present the results of a monitoring study focusing on 20 wells samples collected from the shallow groundwater of Guenniche plain (North Tunisia) during the wet season of May 2016, to present its suitability for drinking purposes with emphasis on the assessment of the presence of nitrate and salinity elements. Nitrate levels' results show that 55% of the samples exceeded the National Tunisian standard limit (NT) and the World Health Organization standard limit (WHO). The salinity results, measured as total dissolved solids (TDS), show that 95% of the samples exceed the international standard, and 25% exceed the national standard. A total of 20% of the wells exceeded the nitrite standards. The total hardness levels indicate that 90% of the samples present very hard water. The Guenniche shallow groundwater average concentrations are categorized as follows: Na+ > Ca2+ > Mg2+ > K+ for the cations and Cl− > SO42− > HCO3− > NO3− for the anions. Nitrate and salinity variations during the period 2006–2015 follow the rainfall fluctuation patterns. The assessment of water quality using Water Quality Index revealed that 95% of the wells' water classes ranged between "poor", "very poor," and "unsuitable for drinking purposes". Therefore, these wells are affected by anthropogenic and/or natural factors and they are inadvisable for drinking purposes, unless the water from these wells undergoes appropriate treatment before use. [ABSTRACT FROM AUTHOR]

This study presents a range of approaches to achieve enhanced characterization of the Zaghouan aquifer system (northeastern Tunisia). Existing water borehole data were analyzed to identify the different reservoir formations, while satellite imagery is analyzed to determinate the superficial lineaments affecting these formations. To define the deep structures determining the geometry of the Zaghouan aquifer system, lithostratigraphic correlations were constructed and analyzed supported by both quantitative and qualitative assessment of gravity measurements. The available lithological columns and their corresponding well logs reveal different carbonate and detritic reservoirs. The carbonate reservoirs consist of Jurassic, Cretaceous and Eocene limestones, whereas the detritic ones are composed of Oligo–Miocene sandstones and Plio-Quaternary to Quaternary sands and gravels. The structural map obtained from processing the satellite imagery confirms several lineaments drawn on the geological map, such as the Zaghouan fault, but also reveals new ones hitherto unrecognized. The intersections of the detected lineaments explain the occurrence of many springs in the area offering potentially favorable opportunities for accessing water resources in fractured aquifers. Analysis of lithostratigraphic correlations shows notable variations in the thickness, depth and composition of reservoir formations. Gravity data interpretation gives more precision by highlighting buried structures and discontinuities with different directions and depths. The delineated tectonic features demonstrate an aquifer system compartmentalized in raised and subsided blocks. The raised compartments may constitute continental divide areas and preferential aquifer recharge zones, while the sunken ones contain a multilayer aquifer composed of Quaternary and Pliocene reservoirs overlying multiple permeable layers, Tertiary and/or Mesozoic in age. [ABSTRACT FROM AUTHOR]

In Tunisia, chemical industries are thought to be the cause of various environmental problems and more particularly the cause of groundwater quality deterioration and contamination. Within this scope, this study assesses the shallow-water quality of the Gabes-North aquifer with regard to the phosphate industry and also to model current and possible future contamination. This allows also the identification of factors that govern the spatial–temporal variation of the main sources of pollution. For that, 60 shallow groundwater samples were collected during the years 2013 and 2014 within and around the industrial chemical phosphate complex of Ghannouche–Gabes. Hydrogeochemical investigation permitted the detection of high concentrations of fluoride and orthophosphates in the sampled waters reaching 12 mg/l and 47 mg/l, respectively. The H2PO4− and F− ion transport model using the Visual MODFLOW software was calibrated and validated by the 2013 and 2014 observed data and was simulated for 6205 days up to the year 2030. The model showed that from 365 to 6205 days, the ions H2PO4− and F− migrated from 100 to 250 m and from 80 to 200 m, respectively, depending on groundwater flow direction. Predictive simulations indicate that the transport rate of these ions can go up to 2.5 times in 2030 compared to those detected in 2014. This integrated investigation in this current study proves that regular pollution constitutes a threat at a given local scale, but can also be used as a reference for reasonable water resources management on a larger scale. [ABSTRACT FROM AUTHOR]

Understanding the controlling factor of groundwater quality could certainly enhance the promotion of the sustainable development of groundwater resources. In fact, during the last decades, the coastal aquifer of Mahdia–Ksour Essef that belongs to the semi-arid region of Tunisia has been marked by an increase of groundwater extraction for irrigation and water for drinking. Moreover, the water quality shows deterioration due to the septic tanks and intensive agricultural activities especially in the coastal side of the aquifer. This study aimed to (1) assess the water quality using Piper Diagram, Box Plot, ions scatter diagrams, (2) understand the processes of mineralization acquisition in the aquifer, and (3) identify the chemical processes and their spatial distribution in the study area. To solve these objectives, the multivariate statistical analysis such as multiple correspondence analysis and hydrochemical analysis was performed. Accordingly, two types of groundwater are identified through the hydrochemical analysis as Na-Cl and Ca-SO4. According to multiple correspondence analysis, three water groups are determined (G1, G2, and G3). Indeed, the groundwater quality is controlled by the water-rock interactions and affected by the seawater intrusion and agricultural activities. The generated results would be helpful to provide a managing model highlighting the threatened locations. It could be considered as a basis for future monitoring programs that aspire to protect water resources. [ABSTRACT FROM AUTHOR]

Water scarcity is a significant issue in the southeastern region of Tunisia, where the sole source of water is from overexploited, salinized, and contaminated aquifers. Despite considerable advancements in studying groundwater hydrochemistry in the study area, Jeffara plain, further investigation is crucial to comprehensively assess groundwater quality in greater depth. The present study investigates the hydrochemistry of the Zeuss-Koutine (ZK) and a part of Mio-Plio-Quaternary (MPQ) groundwater of the Jeffara plain to identify groundwater quality and assess its suitability for drinking and irrigation purposes, as it serves as a vital water source for various sectors. Groundwater samples were collected from 43 exploitation wells and analyzed for temperature, pH, conductivity, major cations (Ca2+, Mg2+, K+ and Na+), major anions (Cl−, HCO3−, NO3−, SO 4 2−), F−, trace elements and NH 4 +. The findings revealed that the groundwater hydrochemical type in the ZK aquifer is dominated by Na–Ca/SO4–Cl, while the MPQ samples fall under the Na–Ca–Mg/SO4–Cl category. Most of samples show too high concentrations of Na+, Ca2+, Cl−, SO 4 2− and Fluoride. The studied groundwaters are highly affected by gypsum dissolution. The WQI indicate that 86% of samples have poor and very poor water quality and 14% are unsuitable for drinking. These findings are further supported by the TH measurements, which classify all water samples as very hard and unsuitable for drinking purposes. Irrigation water quality index indicate that samples fall in severe and high restriction, so, careful attention should be given to the high sodium and salinity content when used in intensive irrigation. The combination of water quality indices and GIS tools is performed to raise awareness among decision makers about groundwater availability and quality in the study area. Additionally, the need to develop strategies for the treatment and preservation of these valuable resources. • Na–Ca/SO 4 –Cl and Na–Cl type dominate Zeuss-Koutine and Mio-Plio-Quaternary samples. • Gypsum dissolution has a significant impact on the studied aquifers mineralization. • 42% and 44% of samples have poor quality and very poor water. • 14% of samples are unsuitable for drinking and 100% are suitable for irrigation. • Water high sodium content points out to prevent an intensive use for irrigation. [ABSTRACT FROM AUTHOR]

In the Kebili region of southern Tunisia, there is increasing demand of water from the Lower Cretaceous Continental Intercalaire (CI) aquifer and the Upper Cretaceous-Miocene Complex Terminal (CT) aquifer. The CI aquifer, given limited low recharge of water and increasing amounts of water extraction, has suffered intense overexploitation since the year 2000. Currently, the sustainability of CI resources is threatened by oil and brine contamination detected at a number of water wells in the Kebili region. Hydrocarbon pollution of the aquifers seems to be ubiquitous because the groundwaters sampled in El Fedjej and Nefzaoua basins exhibit bad water quality according to a number of toxicity indices. Geochemical data indicate that, on a regional scale, groundwater quality, salinity, and dissolved element concentrations are best correlated to petroleum contamination-extraction and to aquifer vulnerability to human perturbations rather than to multiple interactions within the hydrogeological system of the region. The analyses of petroleum compounds in sampled waters indicate that these waters are most consistent with increasing concentrations of organic pollutants; the organic matter is crude and unaltered, testifying to continuous flows of contaminants. The brine contamination, however, is limited to the Djemna water well where the water exhibits a salinity of 20 g L−1. Combined, these findings suggest that groundwater composition in CI water wells in Kebili field is influenced by the migration of hydrocarbons and brine-enriched waters through fractures, and (or) by aquifer decompression. Image 1 • The Oil - brine contamination of CI aquifer is continuous since 2015. • The organic pollutants are made of crude unaltered organic matter. • The water from Djemna borehole has a salinity of 20 g. L−1. • The contamination seems to be attributed principally to natural migration. • The overexploitation enhances contaminant transport. Oil and brine contamination of a number of water wells in the Kebili region (Tunisia) has been continuous since 2015, and it seems to be attributed to natural migration enhanced by aquifer overexploitation. [ABSTRACT FROM AUTHOR]

Abstract Groundwater chemistry depends on a number of natural and anthropogenic processes. Its evolution under natural conditions or in response to human perturbations remains of major concern. Thus, the main purpose of this study is to evaluate the groundwater quality deterioration in Southwestern Tunisia where the increasing water demand is mainly supplied by the deep confined aquifers of SASS (Système Aquifère du Sahara Septentrional) multi-layered system. The permanent exploitation of the deepest Continental Intercalaire (CI) aquifer leaded to increasing water quality deterioration. Recently, the hydrogeological regime of the aquifer system undergoes a tremendous change resulting in hydrocarbon (HC) contamination of the largest aquifer in Southern Tunisia. A mixing of petroleum substances and CI thermal water is currently pumped from a number of CI water boreholes in Kebili region owing to a spectacular on shore hydrocarbon seepage at SW Tunisia. This contamination is attributed to natural migration by continuous upward petroleum flows via permeable faults, plans of weakness and/or leakage through drilling wells (spilled oil). The most noteworthy finding of the current study is that the measured chemical composition of CI aquifer water reveals a significant wider distribution than expected. The impacts of the HC pollution are expressed by scattered geochemical, isotopic and statistical data. The hydrogeochemical results indicate that in the Western field, the CI is characterized by low mineralized water (TDS from 0.6 to 2.7 g/l) while towards the East, the CI water becomes mostly polluted with salinity ranging between 3 and 20 g/l and cadmium (Cd) concentrations between 12 and 90 μg/l these values are widely above the permissible limits for both human consumption and agriculture activities. Similarly, the environmental isotopic fingerprinting indicates that CI thermal waters in the contaminated field are influenced by mixing with deep groundwater. The mixing process seems to be facilitated by regional tectonic features such as deep fractures and major faults in the contaminated area. Correspondingly, the statistical analysis (Principal Component Analysis (ACP) and Hierarchical Cluster Analysis (HCA)) confirm, in turn, the scattered results suggesting the dissimilarity of groundwater composition between the contaminated boreholes and the sampled waters from the western side. Highlights • The used approaches confirm the oil/brine contamination of CI aquifer in El Fedjej basin. • The oil/brine contamination of CI aquifer induces high salinities and enrichment on heavy metals. • The contaminated CI waters in El Fedjej basin are unsuitable for human consumption and agricultural activities. • The overexploitation of CI aquifer is one of the principal factors governing this contamination. [ABSTRACT FROM AUTHOR]

Tunisia has very limited potential of surface and groundwater resources which are subject to different quantitative and qualitative forms of degradation. The risk of groundwater pollution results from the interaction between the vulnerability of aquifers to pollution and anthropogenic activities. Our research focuses on the study of the Sers water table water quality (northwest Tunisia) following the inputs used for agricultural activities in the region. Water samples were extracted from 40 wells to analyze the main physicochemical parameter indicators of the groundwater quality. The results obtained show that these waters have two major facies: Na-Cl and Ca-Mg-SO4. The nitrate contents are relatively high suggesting that the agricultural activities are probably the most important anthropogenic source of water contamination. The results of the Standardized Principal Component Analysis (SPCA) confirm the geochemical methods and results and provide further information about the water quality of the Sers El Kef aquifer. In addition, the pollution degree differs from one site to another depending on the spreading rate of nitrogen fertilizers and the distance from the pollution source. [ABSTRACT FROM AUTHOR]

The Grombalia aquifer (NE Tunisia) is an example of an important source of water supply for regional and national development, where the weak controls over abstraction, fertilizer application and waste disposal, coupled with limited knowledge of aquifer dynamics, is causing aquifer over-exploitation and water quality degradation. Assessing the key role of groundwater in water-resources security is therefore of paramount importance to support new actions to preserve water quality and quantity in the long-run. This study presents one of the first investigations targeted at a complete assessment of aquifer dynamics in the Grombalia aquifer. A multi-tracer hydrogeochemical and isotopic (δ2H, δ18O and 3H) approach was used to study the influence of seasonal variation on piezometric levels, chemical and isotopic compositions, and groundwater recharge. A total of 116 samples were collected from private wells and boreholes during three periods in a 1 year monitoring campaign (February-March 2014, September 2014 and February 2015). Results revealed the overall unsuitability of groundwater for drinking and irrigation purposes (NO3 > 50 mg/L in 51% of the wells; EC >1,000 μS/cm in 99% of the wells). Isotopic balance coupled to piezometric investigation indicated the contribution of the shallow aquifer to deep groundwater recharge. The study also revealed the weakness of ‘business as usual’ management practices, highlighting possible solutions to tackle water-related challenges in the Grombalia region, where climate change, population growth and intensive agricultural activities have generated a large gap between demand and available water reserves, hence becoming a possible driver for social insecurity. [ABSTRACT FROM AUTHOR]

Nitrate contamination still remains one of the main groundwater quality issues in several aquifers worldwide, despite the perduring efforts of the international scientific community to effectively tackle this problem. The classical hydrogeological and isotopic investigations are obviously of paramount importance for the characterization of contaminant sources, but are clearly not sufficient for the correct and long-term protection of groundwater resources. This paper aims at demonstrating the effectiveness of the socio-hydrogeological approach as the best tool to tackle groundwater quality issues, while contributing bridging the gap between science and society. An integrated survey, including land use, hydrochemical (physicochemical parameters and major ions) and isotopic (δ 15 N NO3 and δ 18 O NO3 ) analyses, coupled to capacity building and participatory activities was carried out to correctly attribute the nitrate origin in groundwater from the Grombalia Basin (North Tunisia), a region where only synthetic fertilizers have been generally identified as the main source of such pollution. Results demonstrates that the basin is characterized by high nitrate concentrations, often exceeding the statutory limits for drinking water, in both the shallow and deep aquifers, whereas sources are associated to both agricultural and urban activities. The public participation of local actors proved to be a fundamental element for the development of the hydrogeological investigation, as it permitted to obtain relevant information to support data interpretation, and eventually guaranteed the correct assessment of contaminant sources in the studied area. In addition, such activity, if adequately transferred to regulators, will ensure the effective adoption of management practices based on the research outcomes and tailored on the real needs of the local population, proving the added value to include it in any integrated investigation. [ABSTRACT FROM AUTHOR]

Natural, dissolved 238 U-series radionuclides (U, 226 Ra, 222 Rn) and activity ratios (A.R.s: 234 U/ 238 U; 228 Ra/ 226 Ra) in Continental Intercalaire (CI) groundwaters and limited samples from the overlying Complexe Terminal (CT) aquifers of Algeria and Tunisia are discussed alongside core measurements for U/Th (and K) in the contexts of radiological water quality, geochemical controls in the aquifer, and water residence times. A redox barrier is characterised downgradient in the Algerian CI for which a trend of increasing 234 U/ 238 U A.R.s with decreasing U-contents due to recoil-dominated 234 U solution under reducing conditions allows residence time modelling ∼500 ka for the highest enhanced A.R. = 3.17. Geochemical modelling therefore identifies waters towards the centre of the Grand Erg Oriental basin as palaeowaters in line with reported 14 C and 36 Cl ages. A similar 234 U/ 238 U trend is evidenced in a few of the Tunisian CI waters. The paleoage status of these waters is affirmed by both noble gas recharge temperatures and simple modelling of dissolved, radiogenic 4 He-contents both for sampled Algerian and Tunisian CI and CT waters. For the regions studied these waters therefore should be regarded as “ fossil ” waters and treated effectively as a non-renewable resource. [ABSTRACT FROM AUTHOR]

The suitability of groundwater for drinking and irrigation purposes is potentially disturbed by a variety of factors, including climate change, salinization and risky agricultural practices. The region of Kebilli (Southwestern Tunisia) is marked by an arid climatic condition with a Saharan tendency. However, the spatial partition of the stress factors was not addressed so far in spite of the increasing demand for groundwater to the agricultural and domestic activities which supports the social and economic pressure. Therefore, Water Quality Index (WQI) and Fuzzy Logic models were applied to evaluate the groundwater quality in the Kebilli region for both drinking and irrigation purposes using the geographic information system (GIS) environment to analyze the spatial partition of various factors. According to the analytical results, the calculated values of WQI are between 83.421 and 436.858 for drinking and range from 50 to 77 for irrigation purposes. The prepared Fuzzy spatial maps show that the "desirable" and "acceptable" classes of groundwater quality samples are situated in the center of the studied region, while the "undesirable" quality of groundwater is observed mainly at the Southeastern sectors due to the domestic and agricultural activities besides the over-exploitation of the aquifer. In addition, the Fuzzy membership levels generated into a GIS-based maps give a high correlation of 0.88 and 0.79 with assessed values of WQI for both drinking and irrigation purposes respectively. Grouping analyses also confirm the resulted maps, in turn, the anthropogenic effects coincides globally with the unsuitable areas for both drinking and irrigation purposes. Consequently the perturbations in the fragile environment of the oasis ecosystem are closely related to the deterioration of the groundwater quality and the intensive use of fertilizers and pesticides for agricultural needs in the Kebilli region. The research results may improve the understanding of the groundwater sustainability and as support decision makers for planning the water management and its protection. • Comparison between Fuzzy logic results and WQI gives reliable results. • Fuzzy Logic plays an important role in groundwater quality assessment. • Multi-criteria evaluation approach is powerful to assess the water suitability. • GIS integrated Fuzzy logic and WQI helps delineate appropriate water pumping areas. • The results are helpful to ensure the sustainability of groundwater management. [ABSTRACT FROM AUTHOR]

The Moulares Redeyef Mining basin (MMR-B) is located on Southwestern of Tunisia. The problem of groundwater mineralization in this basin has long been attributed to the significant decline in groundwater reserves. In order to quantify the aquifers reserves and identify processes and factors governing the groundwater quality, a detailed multidisciplinary study was proposed in this study. The approach used various GIS databases, including hydrodynamic characteristics, geochemistry, geology and climatic parameters. A Modflow hydrodynamic model was developed over 67-year modeling period (1953–2020) and many simulations were performed. Water samples were collected from 39 boreholes from the deep aquifer and 13 wells from the superficial aquifer in Tabeddit area. The hydrogeological model shows a flow convergence zone around the Tabeddit area. The reserve of the aquifer system was simulated to 10 Mm3/year for 2020, while it was 26 Mm3/year in 2000. Yet, 61% of exploitable reserves was consumed in 20 years. The quality of groundwater showed that MMR-b is characterized by 4 main trends: Ca–Mg–HCO 3 , Ca–Mg–SO 4 , Na–Cl–NO 3 and Na–Mg–HCO 3. For the heavy metals, the 13 alluvial groundwater samples contain high concentration of Cadmium that exceed the Tunisian Standards. Finally, a Risk Index of Aquifer is elaborated based on the Modflow model and the geochemical quality. The index gives that the PQ layer is under very high risk and the M aquifer is in a moderate situation. Accordingly, it is recommended that the mining deciders revise their exploitation strategy urgently in order to preserve water resources for future use. • Calibration, validation and simulation of a Modflow model under severe climate conditions and anthropogenic activities. • Characterisation of the geochemical composition of groundwater. • Assessment of the contamination of the Plio-Quaternary aquifer with the Phosphates wash rejects. • Proposition a novel risk index for the MMR-b aquifer system. [ABSTRACT FROM AUTHOR]

The Takelsa phreatic aquifer currently shows stress signs and the contamination risk of groundwater by different chemical elements and pesticides is a likely concern. Here we assessed the aquifer vulnerability using the Susceptibility Index (SI) method, considered as a specific vulnerability method that takes into consideration the impact of land uses chemical fertilizers, anthropogenic activities and natural factors as a source of contaminants in groundwater. WetSpass and MODFLOW models were applied to quantify groundwater recharge and water table depth, the two of the most important parameters in groundwater vulnerability mapping. The obtained recharge map for 2015 showed values ranging between 0 and 342 mm/year with an average value of 111 mm/yr, corresponding to about 16% of the annual average rainfall. Regarding the groundwater flow model and for a steady and transient state, a reasonable correlation between the observed and simulated values was obtained confirming that results can be used to establish the vulnerability map. The Susceptibility Index (SI) results showed that the groundwater vulnerability of the studied aquifer ranges from low to very high. Most of the area (90%) has moderate to very high pollution susceptibility mainly due to low slope, agricultural land, high recharge rate, sandy soil dominance and low water table depth. The validation of the obtained map was undertaken through a comparison of areas of high salinity hazard with their relative vulnerability index. For most wells, the different salinity hazard parameters matched with areas of moderate to high vulnerability. The integration between the SI method and WetSpass and MODFLOW models for the study area is a valuable and applicable approach for the assessment of the groundwater vulnerability. • The groundwater vulnerability was assessed with the SI method. • A combination between WetSpass and MODFLOW was used to assess the recharge and the water table depth in the SI model. • The salinity hazard group was used to validate the SI vulnerability map. • Vulnerability maps can provide recommendations for groundwater managers. [ABSTRACT FROM AUTHOR]

This study aimed to analyze the spatial and temporal variations of water quality from 2000 to 2015 in the Grombalia basin aquifer, northern Tunisia. Some physicochemical parameters of collected samples were measured and processed in a GIS environment. Quantitative assessments of their distribution patterns and spatio-temporal variability were performed. Inverse distance weighting (IDW) interpolator and map algebra procedures were the used GIS tools. During 2000, 2015 campaigns 21 groundwater samples were collected from georeferenced boreholes and analyzed for Ca2+, Na+, Mg2+, K+, SO 4 2−, HCO 3 −, Cl−, EC, pH, T°, O 2 , and Salinity. Hydrochemical indices were also estimated such as sodium adsorption ratio, total dissolved solids, and soluble-sodium percentage. Findings were examined in terms of water quality, salinization degree and deterioration rate. During the considered interval, a mixed facies of Cl–SO 4 –Na–Ca, which remained roughly unchanged, characterizes the aquifer. While the spatial distribution of almost all ions is the same, the obtained spatio-temporal maps (2000–2015) for each ion indicate different patterns. Significant variations of concentration were observed in the pediplain area. This region is susceptible to contain most suitable sources for irrigation purposes; it represents 23.8% of groundwater samples that are among the good and safe category. Also, there is no significant variations of water quality indices are observed in the aquifer, except for some northern samples (coastal area). Therefore, a slow hydrochemical process maintains the aquifer quality with a moderate variability while an ongoing salinization hazard locally induces the deterioration level. • Spatio-temporal maps (2000–2015) for each ion indicate different patterns. • Cations/anions exchanges and reverse exchanges were quite evident within the aquifer system. • Over-saturation of Cl− and SO 4 2− impact clearly the aquifer components. • Slow hydrochemical process maintains the aquifer quality with a moderate variability. • Degradation level is induced by high salinization hazards from anthropogenic sources. [ABSTRACT FROM AUTHOR]

In southern Tunisia, environmental threat related to fluorine contamination of the "Complex Terminal (CT)" main aquifer paleogroundwater in one of the most important and strongly vulnerable oases was assessed. Emphasis was placed to hydrogeological and hydrochemical processes controlling the occurrence and the transfer of fluorine to paleogroundwater. It has been demonstrated that the fluorine is released from the Carbonate fluorapatite (CFA) deposit underlying the contaminated aquifer. The liberation of F− is ensured by its exchange with hydroxyl and/or by the CFA dissolution through the passage of hot waters ascending from the deep "Continental Intercalaire (CI)" aquifer. The transfer of F-rich waters to the CT aquifer is occurred mainly through deep faults, aquitard windows and through leakage behind casing. This transfer is due to the potentiometric contrast between the two superimposed aquifers, which is enhanced by anthropogenic processes i.e. the overpumping of the CT groundwater and the CI wellbore integrity failure. Image 1 • Processes for F- contamination of potable groundwater in strongly vulnerable Tunisian oases was assessed. • Fluorapatite (CFA) deposit underlying the contaminated aquifer is identified as the source of fluorine. • Ion exchange with hydroxyl and CFA dissolution are proposed as mechanisms of F- release. • Natural and anthropogenic processes control the transport of high-fluorine water. [ABSTRACT FROM AUTHOR]

Rapid urbanization has several adverse repercussions on the hydrological cycle due to great demands of land and water for housing, transport, health, agriculture, education etc. This paper investigates the impact of the urbanization on the groundwater regime in Sidi Bouzid, an old city located in Central Tunisia under a semi-arid climate where groundwater is the sole source for water needs of the city and the surrounding farming areas. The groundwater vulnerability has been evaluated using the DRASTIC model under a GIS environment. This well-known model is based on the combination of seven parameters, Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone, and hydraulic Conductivity, that are considered as directly controlling the vulnerability of groundwater to potential risks. However, the original model does not consider the effect of urban land uses (urban sprawl and density) on groundwater so a modified DRASTICU model, that includes Urban land use as an eighth parameter has been applied. The net recharge assessment was also modified to include the contribution of leakages from water supply network and sewage networks to the aquifer recharge. On the other hand, soil classes of the aquifer and the vadose zone that are not included in the original listing of the model have been discussed and rated. Sensitivity analysis has been carried out to evaluate the effect of each individual parameter on the vulnerability zoning and to validate the use of each one. The validation of the DRASTICU model was done through the comparison between groundwater vulnerability index and nitrate concentrations. The vulnerability map shows that all the groundwater underlying the city is exposed to pollution risks with vulnerability index varying between extreme in the centre of the city (38%), very high in eastern parts (33.6%) and high (28.4%) elsewhere. Image 1 • Comparative education of urban sprawl on groundwater in Sidi Bouzid city. • Modification of well-kwon DRASTIC model to include urban land uses as an eighth parameter. • Validation of vulnerability zones delimitation by groundwater nitrate contents. [ABSTRACT FROM AUTHOR]