Silicate hydrolysis
"Hydrochemistry, isotope and groundwater modeling to delineate groundwater flow in complex aquifer systems of the upper part of Awaj River (Syria)" Huneau Frederic France (speaker), Asmael Nazeer Syria, Dupuy Alain France, Le Coustumer Philippe France.
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[email protected] Fig.3 Stability diagram of both anorthite and albite and their possible weathering products
The two last diagrams (fig. 3) show that most of the groundwater samples are not in equilibrium neither with anorthite nor with albite, and they will decompose if they are present in the aquifers system as shown in these equations: 2NaAlSi3O8 + 2H2CO3 + 9H2O → Al2Si2O5(OH)4 + 2Na++ 4H4SiO4+ 2HCO3CaAl2Si2O8 + 2H2CO3 + H2O → Al2Si2O5(OH)4+Ca2+ + 2CO32- + 2H+
Hydrochemical facies The piper diagram and the spatial distribution of samples (fig. 4), show that about 70% of these samples tend to have Ca-HCO3 water type. This indicates the short duration of water-rock interaction and the effect of dissolution/precipitation of carbonate rocks as well as recently recharge of groundwater by atmospheric precipitation. The similarity in water type tends to express the existence of a unique hydrochemical.
Abstract The aim of this study was to assess the main features which characterize the hydrogeological system in the western side of Barada and Awaj basin (Syria) based on multi approach methodology using hydrochemistry, environmental stable isotopes and groundwater modeling. The detailed description of hydrogeochemical conditions has underlined the very complex variability of the stratigraphic sequences and hence the numerous hydrogeological units within the study area. Hydrogeochemical evolution reveals the domination of dissolution/precipitation of carbonate rocks as a main mechanism controlling groundwater chemical composition and to less extend, the silicate hydrolysis, dissolution of gypsum and reverse ion exchange. Consequently, hydrochemical patterns did not give enough evidences for the expecting of huge feeding flow from the Jurassic aquifers towards the Neogene/Quaternary aquifer. The similarity in water type tends to express the existence of a unique hydrochemical system hence the individualised groundwater flow paths are difficult to delineate. The isotope compositions imply an important rapid infiltration of atmospheric precipitation mainly throughout the mountainous parts. The study area can be dividing into two main sub-regions, (A) which characterizes by active dissolution phenomena and deep vertical groundwater flow and (B) which characterizes by a shallow horizontal flow component associated with active interaction between groundwater and hosting rocks. The result of groundwater model indicates a hydraulic connection between the deep aquifers and the overlying upper aquifers. The components of the water budget of the upper aquifer had determined. The lateral discharge from the Jurassic aquifer as well as the meteoric recharge is the most important recharging component of this budget. The upward leakage of groundwater from deeper aquifers also plays an important role.
Objectives To gain a better understanding of the groundwater origin and flow system within the framework of its complex geology and morphology of the study area, identify the major hydro-geochemical processes controlling the groundwater quality, and give a quantitative estimation for groundwater budget of the upper aquifer horizon .under steady-state conditions.
Fig.4 modified piper diagram and the spatial distribution show the classification of hydrochemical facies of groundwater.
Local meteoric water line and isotopic composition of groundwater The spatial distribution of precipitation and groundwater stations (fig. 5) indicates the effect of weather front originated from the Mediterranean Sea and the recent recharge of groundwater.
Groundwater modeling to estimate the water budget of the upper aquifer horizon and assess the hydraulic relationship between multilayered aquifers Fig.6 3D model showing water budget in the upper aquifer. The positive inflow and negative outflow values are expressed in Mm3y-1.
Fig. 5 relationship between δ18O and δ2H in the atmospheric precipitation (Weighted Mean) and in the groundwater samples.
Conclusion Fig. 1 Location site of the study area in Barada and Awaj basin, south-western of Syria
Methodology and discussion
Water-Rocks interaction and salts dissolution saturation index of calcite is positive for most of samples whereas it remains negative for most samples in terms of dolomite (fig. 2). Meaning that, on the one hand, precipitation of calcite occurs and on the other hand, saturation with dolomite continues. The saturation indices of gypsum evolves from under-saturated to quasisaturated (fig. 2) indicated the scarcity of gypsum in the aquifers system.
Fig.2 Saturation indices of calcite, dolomite and gypsum as a function of SO4-2 (mmoll-1).
1- The study area has been divided into two main sub-regions A (Jurassic aquifer), and B (Neogene conglomerates and Quaternary alluvial aquifers). 2- The sub-region A is characterised by the karstic features, an active dissolution phenomenon and a deep vertical groundwater flow. 3- The sub-region B is characterized by a shallow horizontal flow. 4- The upward movement from deep aquifers as well as the lateral discharge from the Jurassic karstic aquifer are the important components to maintain the water level in the sub-region B which hosts numerous irrigation wells.
