Complex Terminal Aquifer Research Articles

Geochemical evaluation of fluoride enrichment in the complexe terminal aquifer and its implications for human health in Oued Souf, Algerian Sahara

Geochemical evaluation of fluoride enrichment in the complexe terminal aquifer and its implications for human health in Oued Souf, Algerian Sahara

Advanced approach combines integrated weight water quality index and potential toxic elements for environmental and health risk assessment supported by simulation technique in Oued Souf, Algeria

The current research study evaluated the health and environmental risks issues associated with potentially toxic elements (PTEs) in the complex terminal aquifer located in the Algerian desert. The methods used included principal component and cluster (dendrogram) analysis to estimate source of ions and contamination. Various indices such as the Heavy Metal Pollution Index (HPI), Metal Index, hazard quotient, hazard index (HI), and cancer risk (CR) were applied to assess both environmental and human health risks. Furthermore, the Monte Carlo method was applied for probabilistic assessment of carcinogenic and non-carcinogenic risks through oral and dermal exposure routes in both adults and children. The results revealed that approximately 16% of the samples fell within the low pollution category (HPI < 100), indicating relatively lower levels of heavy metal contamination. However, the remaining 84% of the samples exhibited high pollution levels, indicating a significant presence of heavy metal pollutants in the northeastern part of the investigated area. The calculated average risk index (RI) for the collected samples was 18.99, with a range from 0.03 to 103.21. This indicates that a large portion, 82% of the samples, could cause low ecological risk (RI < 30), whereas the remaining 18% indicate a significant environmental pollution risk. The HI for oral ingestion showed that adults had HI values ranging from 0.231 to 1.54, while children exhibited higher values, ranging from 0.884 to 5.9 (Fig. 5a). For dermal exposure, HI values in adults ranged from 2.71E−07 to 8.74E−06 and in children, from 2.18E−06 to 7.03E−05. These findings highlight the potential non-carcinogenic risks associated with oral exposure to PTEs and underscore the increased vulnerability of children to metals such as Fe, Mn, Pb, and Cr. Most samples showed CR exceeding 1 × 10−4 for chromium (Cr) and lead (Pb), indicating a significant vulnerability to carcinogenic effects in both children and adults.

Hydrogeological characterization of the Complex Terminal aquifer using geoelectrical investigation in the arid environment of Chetma-Biskra (South-East of Algeria)

As a transition hydrogeological area, Biskra (Algeria) holds large groundwater resources in deeply buried aquifers such as the Complex Terminal. Due to a growing demand of drinking water supply and irrigation combined to low recharge, this arid region is facing an acute shortage of water and hence, the need for groundwater investigation. We used an integrated approach including geophysical investigation correlated to the geological and hydrogeological context in the Chetma area. The results highlight a deep structural form with significant hydrogeological features. In fact, two resistant limestone anticlines called Droh corresponding to a piezometric dome and a syncline filled with conductive deposit materials were identified. The Maastrichtian formation, consisting of fractured limestone, about 200 to 350 m thick, together with Lower Eocene marl limestone and limestone form a complex aquifer. At more than 400 m depth, boreholes capturing Maastrichtian limestone offer a high yield ranging from 25 to 90 L/s. Moreover, groundwater yield provides an average of 40 L/s at 300 m of depth. In contrast, synform geometries with high clay and marl content offer a weak groundwater yield. We confirmed the occurence of fractured aquifers which could constitute potentially groundwater production zones. This study provides new insights to enhance groundwater pumping for domestic and irrigation purposes for 2030.

Evaluation of groundwater quality and hydrochemical characteristics in the shallow aquifer of El-Oued region (Algerian Sahara)

The water quality of the aquifer of the El-Oued region (Algerian Sahara) is deteriorating in water quality due to anthropogenic effects and over exploitation of the groundwater resources. This study assesses the quality of groundwater in the El-Oued shallow aquifer for domestic and irrigation purposes and highlights the various geochemical processes that contribute to the mineralization of this water. Twenty-five water samples were collected. The measured and analyzed parameters are: pH, EC, TDS, Na+, K+, Ca2+, Mg2+, Cl−, SO42−, NO3− and HCO3−. The assessment of water potability using the Water Quality Index (WQI) method shows two classes of water quality, namely, the very poor class (8%) and the unsuitable for drinking class (92%). Agricultural water quality was assessed using the parameters; electrical conductivity (EC), sodium adsorption ratio (SAR), sodium percentage (Na %), Kelly ratio (KR), permeability index (PI), magnesium hazard (MH), residual sodium carbonate (RSC) and chloride content. The results showed that the water of this shallow aquifer is unsuitable for irrigation based on EC, Cl− and USSL diagram. This aquifer discloses three facies of water: Cl–Na–Ca (12%), SO4–Na (36%) and SO4–Ca–Mg (52%). In addition, an analysis of physicochemical data obtained from water samples was conducted using correlation matrices, PCA, bivariate plots, and Gibbs diagrams; the saturation indices of the main minerals was also calculated. These analyses have shown that the main reactions responsible for the evolution of water types in the El-Oued shallow aquifer fall into four categories: (1) a mixing process in the waters of deep aquifers (the Complexe Terminal aquifer and the Continental Intercalaire aquifer); (2) the dissolution of salts (in particular, gypsum and halite); (3) cation exchange processes affecting the concentration of Na+, K+, Mg2+, and Ca2+; and (4) anthropogenic influences from domestic sewerage and agricultural activities.

Water quality assessment and hydrogeochemical characterization of the Ouargla complex terminal aquifer (Algerian Sahara)

Water quality assessment and hydrogeochemical characterization of the Ouargla complex terminal aquifer (Algerian Sahara)

Correction to: Water quality assessment and hydrogeochemical characterization of the Complex Terminal aquifer in Souf valley, Algeria

Correction to: Water quality assessment and hydrogeochemical characterization of the Complex Terminal aquifer in Souf valley, Algeria

Water quality assessment and hydrogeochemical characterization of the Complex Terminal aquifer in Souf valley, Algeria

Water quality assessment and hydrogeochemical characterization of the Complex Terminal aquifer in Souf valley, Algeria

Groundwater quality assessment by analytic hierarchy process (geographic information systems-based model) in Souf region (south-east of Algeria)

In this study, we present a method of assessing the quality of groundwater and the Complex Terminal aquifer of the Souf region, under a geographic information systems environment, using the Analytic Hierarchy Process (AHP) model. 20 wells of the study area were sampled for physico-chemical parameters of water quality. These parameters were used in an AHP model to assess the vulnerability of the study area to groundwater pollution. The AHP-weighted overlay analysis was used to identify the areas under the vulnerability classes: admissible, fairly admissible, average and poor. The municipality of Ourmes suffers from alarming pollution due to the importance of agricultural activity, and the use of mineral fertilizers in an irrational manner.

An appraisal of natural fluorine contamination of paleogroundwater in Tozeur oases, southern Tunisia, with emphasis on the anthropogenic impact

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.

Fluoride-bearing groundwater in the complex terminal aquifer (a case study in Hassi Messaoud area, southern Algeria): hydrochemical characterization and spatial distribution assessed by indicator kriging

According to the World Health Organisation (WHO), the human consumption of water containing a high concentration of fluoride (> 1.5 mg/l) can increase significantly many health problems such as dental and skeletal fluorosis. This study investigates fluoride abundance, origin, and its spatial distribution in groundwater from Complex Terminal (CT) aquifer in Hassi Messaoud area (Southern Algeria) where the CT water constitutes the main source of drinking water with a high daily intake. Available water wells were sampled and analysed on their major physico-chemical parameters including fluoride content. Hydrochemical characterization was constrained using the Durov diagram together with a PCA statistical treatment. The saturation indices were computed and used to track fluoride origin. The spatial distribution of fluoride in the studied aquifer was mapped by indicator kriging (IK). The results show that fluoride content ranges from 1.6 to 2.9 mg/l (average = 2.1 ± 0.4 mg/l) exceeding WHO drinking water standards. The Durov diagram, PCA and SI indicate that water acquires mineralization principally by leaching of evaporite minerals. Furthermore, SI evidences that fluoride concentration in water increases with CaCO3 precipitation leading to CaF2 dissolution. IK spatial distribution allows estimating the probability of not exceeding (2.1 mg/l) critical threshold. The cross-validation displays good performance of IK estimation (mean error = 0.05; mean standard error = 0.09). The obtained map shows a low to moderate probability of not exceeding the selected threshold in the whole aquifer. Therefore, the use of CT water for human consumption poses a risk to public health. These results can be used in water management framework and for selecting an ideal position to drill new boreholes for drinking water.

Uranium isotopes as tracers of groundwater evolution in the Complexe Terminal aquifer of southern Tunisia

The Complexe Terminal (CT) multi-layer aquifer is formed by Neogene/Paleogene sand deposits, Upper Senonian (Campanian-Maastrichtian limestones) and Turonian carbonates. The chemical composition and isotopes of carbon and uranium were investigated in groundwater sampled from the main hydrogeological units of the (CT) aquifer in southern Tunisia. We paid special attention to the variability of uranium contents and isotopes ratio (234U/238U) to provide a better understanding of the evolution of the groundwater system. Uranium concentrations range from 1.5 to 19.5 ppb, typical of oxic or mildly reducing conditions in groundwaters. The lowest concentrations are found southeast of the study area, where active recharge is supposed to take place.When looking at the isotope composition, it appears that all the samples, including those from carbonate levels, are in radioactive disequilibrium with significant 234U excess. A clear-cut distinction is observed between Turonian and Senonian carbonate aquifers on the one hand, with 234U/238U activity ratios between 1.1 and 1.8, and the sandy aquifer on the other hand, showing higher ratios from 1.8 to 3.2. The distribution of uranium in this complex aquifer system seems to be in agreement with the lithological variability and are ultimately a function of a number of physical and chemical factors including the uranium content of the hosting geological formation, water-rock interaction and mixing between waters having different isotopic signatures. Significant relationships also appear when comparing the uranium distribution with the major ions composition. It is noticeable that uranium is better correlated with sulfate, calcium and magnesium than with other major ions as chloride or bicarbonate.The 14C activities and δ13C values of DIC cover a wide range of values, from 1.1 pmc to 30.2 pmc and from −3.6‰ to −10.7‰, respectively. 14C model ages estimated by the Fontes and Garnier model are all younger than 22 Ka and indicate that the recharge of CT groundwater occurred mainly during the end of the last Glacial and throughout the Holocene.

Hydrogeochemical characterization of the Complexe Terminal aquifer system in hyper-arid zones: the case of wadi Mya Basin, Algeria

The groundwater resources management of the wadi Mya basin, located in the North East of the Algerian Sahara and witnesses a hyper-arid climate, poses salinity problems. In order to identify the mechanisms involved in causing these problems, physicochemical analyses were performed on 114 water samples. The hydrogeological system of Complexe Terminal of the wadi Mya basin is very weakly recharged and contains two highly mineralized aquifer levels. These are the Mio-Pliocene sands aquifer and the underlying Senonian carbonates aquifer. They are separated to a great extent by an intermediate evaporitic Eocene layer. Both aquifers show analogous hydrochemical facies indicating, thus, intercommunication between them. The overall mineralization is dominated by chloride sulfate, sodium and magnesium facies and is explained by the dissolution of the evaporitic components of the intercalations in the aquifer matrix, but also by the old character (fossil) of water and cationic exchange reactions resulting from water-rock interactions over time. The salinity variation exhibit a trend that conform to the groundwater flow direction. Vertical transfer of water, sometimes saltier downward from the phreatic aquifer, sometimes softer upward from the deep Albian sandstone aquifer, was noticed. Areas of low mineralization were also identified in the western edge of the basin, where wadi’s floods, which drain the eastern side of the M’zab dorsal, are wide spread.

Causes and risk evaluation of oil and brine contamination in the Lower Cretaceous Continental Intercalaire aquifer in the Kebili region of southern Tunisia using chemical fingerprinting techniques

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.

Groundwater salinization survey of the Upper Cretaceous-Miocene Complexe terminal aquifer in the Sabaa Biar area of southwestern Tunisia

An integrated hydrogeological study involving the Schlumberger depth sounding method, geological data and wells data was conducted at the Sabaa Biar area of southern Tunisia to elucidate the problem of increasing groundwater salinity within The “Complexe Terminal”. The “Complexe Terminal” aquifer near Sabaa Biar region is a bi-layered aquifer comprised of fractured limestones of the Cretaceous (Campanian–Maastrichtian) Berda Formation and sandstone of the Miocene Beglia Formation. The aquifer is affected by a main NW–trending fault, which is a chemical barrier that divides the study area into eastern and western blocks delivering freshwater and saline water, respectively. The salinization of groundwater within the limestone (Campanian–Maastrichtian Berda Formation) is linked mainly to the dissolution of outcropping Coniacian–Santonian gypsum along the core of the Jebel Sidi Bouhlel anticline to the east of the study area. Meteoric water dissolves salt from outcropping gypsum, flows through the fractures networks, and recharges the fractured limestone of the upper Berda Formation. The mobilization of salts stored in the salt-rich Quaternary sediment on hillslopes and inchannels contributes also to the salinization of groundwater within the sandstone (Miocene Beglia Formation) by lateral infiltration subsequent to water drainage during the wet season. The over exploitation of water from the Miocene sandstone causes an influx of saline-rich water from the underlying limestone of the Berda Formation into the sandstone of the Beglia Formation. Other sources of salinization of groundwater (such as ascension of hypersaline water from deep aquifer along faults, and the return flow of irrigation waters in the Djerid region) have been documented in this region, but are not discussed in this paper.

Hydro-geochemical processes in the Complexe Terminal aquifer of southern Tunisia: An integrated investigation based on geochemical and multivariate statistical methods

Hydrochemical data from a total of 104 groundwater samples were used to investigate the main factors and mechanisms that control the chemistry of groundwaters in the Complexe Terminal (CT) aquifer of Chott region in southern Tunisia. Multivariate statistical techniques combining Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) were applied to the dataset of 12 physicochemical parameters (i.e. pH, T°, depth, Na+, K+, Ca2+, Mg2+, HCO3−, NO3−, Cl−, SO42−, and TDS). The HCA using Ward’s method and squared Euclidean distance classified the parameters into four clusters based on their dissimilarities. The application of PCA resulted in two factors explaining 64.25% variance. Geochemical methods combined with HCA and PCA confirm that groundwater chemistry is not controlled by the different lithological facies of the aquifer, but by the presence of evaporates randomly distributed in the basin.Although stable isotope data (2H and 18O) of some groundwater are consistent with a slight modern recharge, CT groundwaters are mostly depleted bearing witness to the recharge of the aquifer system occurred under different climatic conditions than present. The stable isotopic composition of these paleowaters which all lie to the right of the local meteoric water line also indicates more pronounced evaporation of rainfall during the recharge process than during present-day conditions.

Evaluation of Temperature and Mixing Process of Water in Deep and Shallow Aquifers in the Southwestern Tunisia: Case of Djerid Region

This study addresses the hydrogeochemistry of thermal and cold waters circulating in the mineralised area of the Djerid basin (South-western of Tunisia) that aimed basically at understanding the mixing processes influencing their chemical compositions. Temperature intervals are 38–75 and 24.5–26.8 °C for thermal water and cold water, respectively. Two distinct hydrogeological systems supply water either for irrigation or for drinking; they are: (1) the Continental Intercalaire geothermal aquifer (CI), and (2) the Complex Terminal aquifer (CT). Geological, geophysical, hydrogeological, hydrochemical methods are applied to reliably analyze and understand the operating model of the aquifer systems, to determine the hydrogeological, the geochemical behaviours, and the possible inter-aquifers water transfer in south western of Tunisia. The reservoir temperature is estimated to be between 60 and 104 °C according to calculations using silica geothermometers and computation of saturation indexes for different solid phases. Based on chemical and thermal data, it is hypothesized that: (1) mixing rate, which occurs between the ascending deep geothermal water and shallow cold water, is estimated from the enthalpy and chloride methods to be about 65 and 73 % respectively, (2) Mixing models can explain the temperature of the geothermal fluid component.

Environmental isotopes as the indicators of the groundwater recharge in Tunisian Chotts region

Hydrogeological investigations in arid zones tend to be logistically difficult and costly. However, isotopic techniques can be used to gain valuable reconnaissance information, for example, in advance of new drilling programmes and also during exploitation. Thus, the most cost-effective exploration in arid zones will include both good hydrogeological data combined with isotopic and supporting geochemical information. The question of recharge is one of the most critical for groundwater management in dry areas. Is the recharge currently taking place and at what rate? If recharge is occurring, further important problems arise dealing with possible mechanisms of recharge, which may occur through direct infiltration, upward leakage, lateral recharge from areas of rainfall, and lateral seepage of river (Fontes and Edmunds, Technical documents in hydrology 77, 1989). In this study, which is of interest for an important aquifer system in southern Tunisia, conjunction of environmental isotopes, i.e.: 18O, 2H, 3H, 14C and 13C and chloride contents was used to understand the mode of recharge of the shallow Plio-Quaternary (PQ) and the intermediate Complexe Terminal (CT) aquifers. Both are unconfined in the vicinity of the Tozeur uplift and the Dahar upland and show relatively modern water that originated from present-day rainfall. It has been demonstrated that the Continental Intercalaire deep groundwater contributes to the CT aquifer recharge, the latter to the upper PQ shallow aquifer. The shallow PQ is mainly recharged by return flow irrigation and upward leakage in oases areas. Away from oases zones, sporadic recharge may occur at the inter-dunes especially between the Chott Djerid and Chott El Gharsa, in the Bir Roumi region and in the Kebili sand fields.

Nitrate contamination in groundwater in the Sidi Aïch–Gafsa oases region, Southern Tunisia

Groundwater pumped from the semi-confined Complex Terminal (CT) aquifer is an important production factor in irrigated oases agriculture in southern Tunisia. A rise in the groundwater salinity has been observed as a consequence of increasing abstraction from the aquifer during the last few decades. All sources of contamination were investigated using hydrochemical data available from the 1990s. Water samples were taken from wells tapping both the CT and the shallow aquifers and analyzed with regard to chemistry tracers. Hydrochemical and water quality data obtained through a sampling period (December 2010) and analysis program indicate that nitrate pollution can be a serious problem affecting groundwater due to the use of nitrogen (N) fertilizers–pesticides in agriculture. The concentration of nitrate in an groundwater-irrigated area in Gafsa oases basin was studied, where abstraction from an unconfined CT aquifer has increased threefold over 25 years to 34 million m3/year; groundwater levels are falling at up to 0.7 m/year; and groundwater is increasingly mineralised (TDS increase from 500 to 4,000 mg/L), with nitrate concentrations ranging from 16 to 320 mg/L.

Properties of geothermal resources in Kebilli region, Southwestern Tunisia

The Kebilli region is located in the Southwestern part of Tunisia, and is characterized by the presence of deep and shallow geothermal systems (continental intercalary and complex terminal). Chemical and isotopic contents are used to classify the type and determine the origin of thermal water. An evaluation of reservoir temperature and a possible geothermal fluid mixing are also carried out. Both continental intercalary-deep aquifer and complex terminal-shallow aquifer are of Na–(Ca)–Cl–(SO4) mixed water type. The use of different geothermometers and the computation of saturation indexes for different solid phases suggests that the thermal reservoir temperature of the continental intercalary is between 92 and 105 °C, while the fluid temperature from the shallow complex terminal aquifer ranges from 50 to 75 °C. Also, the isotopic data indicates the old origin of all groundwater of Southwestern Tunisia. Mixing effects characterizing the continental intercalary and the complex terminal aquifers were identified using δ2H and δ18O relationship. It appears that the upward movement of thermal water from the deep aquifer to shallow ones is probably due to the abundant fractures in the research area.

Deciphering groundwater flow between the Complex Terminal and Plio-Quaternary aquifers in Chott Gharsa plain (southwestern Tunisia) using isotopic and chemical tools

The Complex Terminal (CT) and Plio-Quaternary (P-Q) aquifers in the Chott Gharsa plain in southwestern Tunisia have been investigated with the aid of chemical and isotopic tools. It has been demonstrated that groundwater from the CT is mainly of palaeo-origin, especially in the western and central parts of the plain where the most negative values of δ18O and δ2H were observed (between −8.1 and −7.6‰ for δ18O, and −60 to −57‰ for δ2H), combined with low concentrations of radiocarbon (6.8–7.5 pmc) and absence of tritium. Modern recharge of the aquifer occurs only in the eastern part of the system where younger waters were observed, as indicated by their stable isotope composition, relatively high radiocarbon content and presence of tritium. Groundwater from the P-Q multi-layer aquifer represents mixtures of ascending deep CT waters and modern water recharging the P-Q aquifer system. Isotope mass balance was used to quantify mixing proportions. The calculations showed that the contribution of deep CT groundwater to the P-Q aquifer system reaches about 75% in the western and central parts of the plain where the CT aquifer remains strongly artesian. This contribution decreases to about 15% towards the eastern part of the plain, as a consequence of significant reduction of artesian pressure in this area of the CT aquifer. Chemical data suggest that mineralization of the studied groundwater systems is controlled mainly by dissolution of evaporative minerals (halite, anhydrite and gypsum) and cation exchange reactions with the matrix, possibly enhanced by recent anthropogenic disturbance of the system caused by lowering of the water table due to heavy exploitation and return flow of saline irrigation water into the P-Q aquifer. Editor D. Koutsoyiannis; Associate editor E. Custodio Citation Yangui, H., Abidi, I., Zouari, K., and Rozanski, K., 2012. Deciphering groundwater flow between the Complex Terminal and Plio-Quaternary aquifers in Chott Gharsa plain (southwestern Tunisia) using isotopic and chemical tools. Hydrological Sciences Journal, 57 (5), 967–984.