Effect of Water and Leachate on Hydraulic Behavior of Compacted Bentonite,Calcareous Sand and Tuff Mixtures for Use as Landfill Liners

Compacted soil–bentonite liners, consisting of a sandy soil mixed with bentonite as backfill, are used extensively as engineered barriers for contaminant containment. This paper studies the valorization of local materials containing calcareous sand, tuff obtained from Laghouat region (in the South Algeria), to associate with bentonite in order to improve their hydraulic characteristics for use as landfill liner material. Firstly, a geotechnical characterization of mixtures chooses from a fixed percentage to 10% bentonite and different percentages of calcareous sand and tuff so that they are complementary to 90% by not 10%. Thereafter, the determination of saturated hydraulic conductivity at falling-head permeability (K_v) and oedometer (K_id, indirect Measure) tests of all compacted mixtures at Optimum Normal Proctor have been carried out using both permeates by tap water and a landfill leachate in order to simulate long-term conditions. The results showed that the saturated hydraulic conductivity of tap water is relatively lower than the one saturated by leachate in the falling-head test, unlike the oedometer test. The B₁₀CS₂₀T₇₀ mixture has satisfied the hydraulic conductivity criterion of bottom barriers (i.e. water permeated: k_v20° = 1.97 × 10^?9 and k_id from 7 × 10^?9 to 1.83 × 10^?10 < 10^?9m/s; leachate permeated: k_v20° = 2.91 × 10^?9 and k_id from 7 × 10^?9 at 1.44 × 10^?10 < 10^?9 m/s). Finally, a comparison between direct measurements of the saturated hydraulic conductivity by triaxial (K_d) test and oedometer test (K_id) in the range of effective stress applied 100–800 kPa led to propose equations of correlations between these two methods. In conclusion, adopted formulation B₁₀CS₂₀T₇₀ perfectly meets the regulatory requirements in force and constitutes an economic product based on available local materials for engineers barriers.     

The elimination of the 1:2 critical terms of a first order theory of Uranus perturbed by Neptune through Von Zeipel method

In this paper we eliminate in a first order U-N theory the 1 : 2 critical terms up to the third degree with respect to eccentricity — inclination in both parts, main and indirect of the U-N planetary Hamiltonian. We operate the Von Zeipel technique. We adopt, in this theory, the Jacobi-Radau coordinates, and the Poincaré canonical variables. We neglect powers higher than the third in the eccentricity-inclination. This paper is related to the two previous articles (Kamel, 1982; 1983).     

A note on the Hori-Lie perturbation technique

In this paper we describe how to avoid the introduction of Hori's pseudo time in general planetary theory in the case of two planets.     

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

Abstract

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.     

Application of environmental tracers to study groundwater recharge in a semi-arid area of Central Tunisia

Abstract

Groundwater of the Tertiary-Quaternary Formations in the Jeloula basin (Central Tunisia), together with rain and surface waters, were analysed to investigate the mineralization processes, the origin of the water and its recharge sources. The water samples present a large spatial variability of chemical facies which is related to their interaction with the geological formations. The main sources of the water mineralization are the dissolution of evaporitic and carbonate minerals and cation exchange reactions. Stable isotopes indicate that most groundwater samples originate from infiltration of modern precipitation. Surface water samples from small dam reservoirs show a ¹⁸O/²H enrichment, which is typical of water exposed to open-surface evaporation in a semi-arid region. Considerable data of ³H and ¹⁴C allow the qualitative identification of the present-day recharge that is probably supplied by infiltration of recent flood waters in the Wadi El Hamra valley, and by direct infiltration of meteoric water through the local carbonate outcrops.

Editor D. Koutsoyiannis; Associate editor S. Faye     

Use of Landsat 7 ETM+ for lithological and structural mapping of Wadi Afara Heouine area (Tahifet–Central Hoggar, Algeria)

Wadi Afara Héouine area (Tahifet, Central Hoggar) is marked by the existence of very diversified lithologies affected by big submeridian accidents, of which Wadi Afara Héouine, who represents a "linear discontinuity" on near 80 km forming a morphological limit which separates, a strongly gneissic domain (Oua Hellèdjène) of a domain with metasedimentary dominant (Aghefsa). Lithologies not described in the former works were defined by the application of specific treatments (color composite, band ratios, and selective PCA). They also allow us to suggest some modifications to the geologic map of Tahifet. Directional filters associated to the previous treatments helped us in the elaboration of lineament map which accentuates the various accidents affecting the region. It seems clearly that treatments applied to the images ETM contribute in an undeniable way to the geologic study of this region especially since a big part of this region is inaccessible     

Hydrologic and geologic factors controlling groundwater geochemistry in the Turonian aquifer (southern Tunisia)

Water in the fissured limestone and dolomite of the Turonian aquifer of Tunisia has been investigated using geochemical (major ions) and isotopic (δ¹⁸O, δ²H, ¹⁴C) data. To carry out a characterization of aquifer behaviour, 48 representative samples were collected at the end of the humid season. The evolution of chemical composition of groundwater from recharge areas to discharge areas is characterized by increasing sodium, chloride and sulphate contents as a result of leaching of evaporite rock. In the study, three distinct chemical trends in groundwater were identified. The major reactions responsible for the chemical evolution of groundwater in the investigated area fall into three categories: (1) calcite precipitation, (2) gypsum and halite dissolution, and (3) ion exchange. The stable isotope composition of water samples indicates large-scale interaction between the Continental Intercalaire and the Turonian aquifer and the presence of a young local component which probably enters the system via faults and/or fractures.     

The role of gender and age in fracture distribution following the 2008 Wenchuan earthquake

This study explored demographic variations among victims injured in the 2008 Wenchuan earthquake. The study analyzed records of 2,148 patients who were hospitalized with earthquake-related injuries in 14 hospitals between May 12 and May 21 of 2008. We tested the effects of gender and age on the incidence of fractures and amputations. Although more women than men were hospitalized as earthquake victims, the results indicated that a higher incidence of pelvic fracture in women was the only statistically significant injury with regard to gender. Age had a more complex effect on the rate and pattern of fractures. Children younger than 15 years old were the most likely to sustain skull fractures and amputations. The elderly were the most likely to be associated with limb fractures. Adult men were the most likely to suffer spine fractures and adult women rib fractures. The paper concludes with an interpretation of the results in the context of China’s rural conditions and discusses implications for post-disaster emergency operations and planning.     

Hydrogeochemical processes affecting groundwater in an irrigated land in Central Tunisia

Detailed hydrogeochemical investigation has provided new information concerning the major factors and mechanisms controlling the groundwater chemistry of Chougafiya basin. The hydrogeochemical characteristics of groundwaters comprise three main types: Cl–SO₄–Ca, Cl–SO₄–Na and Cl–Na. Hydrochemical characteristics based on the bivariate diagrams of major (Cl^?, SO₄ ^2?, NO₃ ^?, HCO₃ ^?, Na⁺, Mg²⁺, K⁺ and Ca²⁺) and some trace (Br^? and Sr²⁺) ions, mineral saturation indices and hierarchical cluster analysis indicate different origins of groundwater mineralization. The water–rock interaction (dissolution of evaporitic minerals), followed by cation exchange reactions with clay minerals, constitute the main processes that control groundwater salinization. However, the chemical composition of brackish groundwater in the central and southern parts of the study area is influenced by a mixing process with Sabkhas salt groundwater. The mixing proportions inferred from chloride mass balance prove that the contribution of Sabkhas groundwater to Quaternary aquifer ranges between 2.7 and 9.1 %. These intrusion rates reflect the progress of the saltwater–freshwater interface, which is mainly controlled by the piezometric level variation and the distance to the Sabkhas.     

Deciphering interaction of regional aquifers in Southern Tunisia using hydrochemistry and isotopic tools

Groundwater is the most important source of water supply in southern Tunisia. Previous hydrogeologic and isotopic studies carried out in this region revealed the existence of two major aquifer systems: the “Complex Terminal” (CT) and the “Continental Intercalaire” (CI). Turonian carbonates constitute one of the major aquifer levels of the CT multilayered aquifer. It extends over most of southern Tunisia, and its hydrodynamic regime is largely influenced by tectonics, lithology and recharge conditions. Forty-eight groundwater samples from the CI and Turonian aquifers were collected between January and April 2004 for chemical and isotopic analyses. Hydrochemistry and isotopic tools were combined to get an insight into the processes controlling chemical composition of groundwater and wide-scale interaction of these two aquifer systems. Analysis of the dissolved constituents revealed that several processes control the observed chemical composition: (i) incongruent dissolution of carbonate minerals, (ii) dissolution of evaporitic minerals, and (iii) cation exchange. Dissolution alone cannot account for the observed high supersaturation states of groundwater with respect to calcite and dolomite. The observed supersaturation is most probably linked to geogenic CO₂ entering water-bearing horizons of the CT and CI aquifers via deep tectonic faults and discontinuities and subsequent degassing in the exploitation wells. Presence of geogenic CO₂ in the investigated region was confirmed by C isotope data of the DIC reservoir. The radiocarbon content of the Turonian samples varied between 9.5 and 43 pmc. For CI samples generally lower values were recorded, between 3.8 and 22.5 pmc. Stable isotope composition of Turonian groundwater samples varied from −8.3 to −5.3‰ for δ¹⁸O and from −60 to −25‰ for δ²H. The corresponding ranges of δ values for the Continental Intercalaire samples were from −8.9‰ to −6.9‰ for δ¹⁸O and from −68.2‰ to −45.7‰ for δ²H. Stable isotope composition of groundwater representing CT and CI aquifers provide strong evidence for regional interaction between both systems.