A hydrochemical study of the Hammam Righa geothermal waters in north-central Algeria

This study focuses on the hydrochemical characteristics of 47 water samples collected from thermal and cold springs that emerge from the Hammam Righa geothermal field, located in north-central Algeria. The aquifer that feeds these springs is mainly situated in the deeply fractured Jurassic limestone and dolomite of the Zaccar Mount. Measured discharge temperatures of the cold waters range from 16.0 to 26.5 °C and the hot waters from 32.1 to 68.2 °C. All waters exhibited a near-neutral pH of 6.0–7.6. The thermal waters had a high total dissolved solids (TDS) content of up to 2527 mg/l, while the TDS for cold waters was 659.0–852.0 mg/l. Chemical analyses suggest that two main types of water exist: hot waters in the upflow area of the Ca–Na–SO₄ type (Hammam Righa) and cold waters in the recharge zone of the Ca–Na–HCO₃ type (Zaccar Mount). Reservoir temperatures were estimated using silica geothermometers and fluid/mineral equilibria at 78, 92, and 95 °C for HR4, HR2, and HR1, respectively. Stable isotopic analyses of the δ¹⁸O and δD composition of the waters suggest that the thermal waters of Hammam Righa are of meteoric origin. We conclude that meteoric recharge infiltrates through the fractured dolomitic limestones of the Zaccar Mount and is conductively heated at a depth of 2.1–2.2 km. The hot waters then interact at depth with Triassic evaporites located in the hydrothermal conduit (fault), giving rise to the Ca–Na–SO₄ water type. As they ascend to the surface, the thermal waters mix with shallower Mg-rich groundwater, resulting in waters that plot in the immature water field in the Na–K–Mg diagram. The mixing trend between cold groundwaters from the recharge zone area (Zaccar Mount) and hot waters in the upflow area (Hammam Righa) is apparent via a chloride-enthalpy diagram that shows a mixing ratio of 22.6 < R < 29.2 %. We summarize these results with a geothermal conceptual model of the Hammam Righa geothermal field.     

Determination of the origin of mineralization and groundwater salinity in the Adrar region in the southwest of Algeria

To some extent, the sedimentary sequence with the largest groundwater reserves in northern Sahara is marked by a certain water table level, regionally known as the "Continental Intercalaire"(CI). "Continental Intercalaire"(CI) refers to "Continental Intercalary" widely distributed among three countries. Algeria, Tunisia and Libya, which have significant potential of water resources. As it is the only water resource relatively easily accessible to the inhabitants of the Sahara, it is widely developed. The physico-chemical characteristics of statistical processing in principal component analysis(PCA) and the chemical phase measurement of groundwater in the unconfined aquifer captured by "Foggaras"(traditional system irrigation composed of well system linked by a horizontal channel from their bases) and the deep drillings located in the study area were accessible. Therefore, there were some favorable conditions for comparing the chemistry of these waters with the standards of potability established by the World Health Organization. Then, the study detected the origin of excessive mineralization and the excessive content of Na, Cl, K, Mg and Ca that originated from the leaching of the clay and carbonate layers of the "Continental Intercalaire". In addition, the enrichment in NO_2~-, NO_3~- and SO_4~(2-) was due to the excessive use of fertilizer in the whole region for shallower Foggaras waters, and this study also showed the dominant chemical facies of groundwater related to the significant abundance of these mineral salts in this thick aquifer horizon.     

Influence of Electrokinetic Process on Compressibility Behaviour of Salt Affected Soils

Geotechnical and Geological Engineering - The improvement of salt affected lands is a major environmental challenge in arid and semi arid regions all over the world. Electrokinetic treatment is one...     

New information on radionuclides concentration in phosphorites originating from Tunisia and Algeria

In this study we investigate the radiological hazard of naturally occurring radioactive material in Tunisian and Algerian phosphorite deposits. Eight samples of phosphorite were collected from the phosphorite mines. The Tunisian and Algerian phosphorites occur in the Late Paleocene and Lower Eocene (Ypresian-Lutetian) in age (Béji Sassi 1984 and Zaïer 1999). Activity concentrations in all the samples were measured by alpha spectrometry and gamma spectrometry. Alpha spectrometry analyses show that the specific activity values of ²³⁸U, ²³⁴U and ²³⁵U in the samples of Tunisian phosphorite were 327?±?7 (321–327), 326?±?6 (325–331) and 14.50?±?0.72 (13.90–15.57) Bq kg^?1, respectively. Specific activity measured by gamma spectrometry in the samples of the Tunisian and Algerian phosphorite shows a small difference. Specific activity levels of ⁴⁰K, ²²⁶Ra, ²³²Th, ²³⁵U and ²³⁸U in the phosphorite samples from Tunisia were, respectively, 71.10?±?3.80, 391.54?±?9.39, 60.38?±?3.74, 12.72?±?0.54 and 527.42?±?49.57 Bq kg^?1 and Algeria were 15.72?±?1.73, 989.65?±?12.52, 12.08?±?1.20, 47.50?±?1.52 and 1,148.78?±?7.30 Bq kg^?1, respectively. The measured value of specific activity of ²³²Th and ⁴⁰K in the Tunisian phosphorite samples is relatively higher than that found in the samples of Algerian phosphorite. The measured activity of uranium (²³⁸U) in the Tunisian phosphorite (527?±?49) Bq kg^?1 is lower than in Algerian phosphorite. The measured activity of ²³⁸U in the Tunisian phosphorite samples was (527–1,315?±?65) ²³⁸U Bq kg^?1 which is higher than its maximum background value of 110 Bq kg^?1 in soils of the various countries of the world (Tufail et al. Radiat Meas 41:443–451, 2006). Different geological origins of phosphorites deposits are the main reason for the large spread in worldwide specific activities. The obtained results of uranium concentrations in phosphorites of different types (Algerian and Tunisian) demonstrate that the uranium concentrations are mainly governed by the phosphatic material. The present study reveals that phosphorite deposits contain natural radioactivity higher than background level.     

GIS-based evaluation of groundwater quality and estimation of soil salinization and land degradation risks in an arid Mediterranean site (SW Tunisia)

Arabian Journal of Geosciences - The present work is concerned with the valorization of clay minerals of the Aleg formation (Coniacian-middle Campanian) in the clinker manufacturing. The studied...     

Processus de minéralisation de la nappe du Plio-Quaternaire dans la plaine de Segui-Zograta (Sud-Ouest tunisien)

Résumé

La plaine de Segui-Zograta est une cuvette synclinale à remplissage Mio-Plio-Quaternaire où la nappe du Plio-Quaternaire constitue la principale source d’approvisionnement en eau pour l’abreuvement du chaptel et pour l’agriculture. Cette zone présente une hétérogénéité de répartition de la minéralisation des eaux souterraines. L’investigation des outils géochimiques basée sur l’étude des éléments majeurs, des isotopes stables (¹⁸O, ²H) et radioactifs (³H, ¹⁴C) indique la combinaison de différents processus contrôlant la minéralisation de ces eaux. Dans la partie Ouest, les eaux du Plio-Quaternaire présentent un facies de type sulfato-calco-sodique et des salinités élevées. Elles subissent l’effet de la dissolution des minéraux évaporitiques et résultent du mélange par drainance ascendante des eaux fossi des aquifères les plus profonds, à salinité élevée et à faciès chloruro-sulfato-sodique, à travers la faille d’Om Ali où leur contribution peut atteindre 96%. Dans la partie Est, ces eaux sont de type sulfato-calcique, considérées relativement moins minéralisées que celles de la partie Ouest. Elles sont issues de l’infiltration des eaux de pluie récentes et qui ont subi l’effet de l’évaporation.

Editeur Z.W. Kundzewicz     

Coupled dynamic elastic–plastic analysis of earth structures

A fully coupled finite element code based on mixture theory is developed. Prévost's multi-surface constitutive model is tailored to three-dimensional loads and used to predict effective stresses. A new viscous boundary is implemented to avoid wave reflections towards the structure. In contrast to traditional methods, this boundary is able to absorb the two dilatational waves and the shear wave.Two soil deposits and two dams, with different slopes, composed by loose and dense sands have been subjected to the Pacoima accelerogram. Results show how the liquefaction propagates in the soil deposits and earth dams. The importance of the coupling between dilatancy–contractancy and filtration is highlighted by a parametric investigation. Phenomena such as liquefaction and cyclic mobility are reproduced, indicating the robustness of the constitutive model and finite element simulations. As an outcome of the parametric analysis, the seismic stability of dams cannot be improved by decreasing the upstream or downstream slopes.     

A viscous boundary for transient analyses of saturated porous media

An absorbing boundary for saturated porous media is developed that can be used for transient analyses in the time domain. The elastic constitutive equations for the saturated porous media follow Bowen's formulation. The method consists of applying viscous tractions along the artificial boundary. The absorbing boundary behaviour is assumed linear and isotropic. Hadamard's conditions provide the speeds of the dilatational and shear waves that propagate in saturated porous media. Since these expressions are frequency independent, the intensities of the viscous tractions are evaluated in the time domain, and the two dilatational waves are accounted for. The viscous tractions are defined from the drained characteristics, assuming an infinite permeability, at variance with the traditional ‘undrained’ method based on undrained characteristics and a null permeability. Solid media and materials with low permeability are also retrieved as subcases. The results show that, at no additional cost, this ‘drained’ method is more accurate for all permeabilities than the ‘undrained’ method, which disregards the existence of the second dilatational wave. Copyright © 2003 John Wiley & Sons, Ltd.     

Characterization of organic matter deposited in the oriental zone from Moknine hypersaline environment, oriental Tunisia

The geochemistry data show that the total organic carbon （TOC） contents are high in the surface sediments in the eastern part of the Moknine＇ s Sebkha. Low decreasing of organic matter （ OM ） with increasing depth indicates the good preservation of OM in modern sediments. ＂Lignite levels＂ inserted in the sand sequence and deposited at the edge and in the intermediate zone are considered as lithologic and organic markers. It is characterized by high TOC and poor hydrogen index （HI） , indicating a higher plant origin and good preservation of OM in thin beds under anoxic condition. In all samples low values of HI are typical for strong terrigenous input in the Sebkha. Gas chromatography （GC） of saturate fraction showed that OM in the border zone is provided from plants but in the central zone OM is a mixture of terrestrial fraction and little fraction from microalgae. The study of free lipids indicated that this environment was influenced by intense bacterial and microbial activities, as evidenced by the abundance of n-alkanes and nC18-nC22.