Abstract
The Triassic aquifer is located in southereastern Tunisia, in the Medenine region, and being part of Jeffara's multilayer aquifer system. The aquifer is currently overexploited with an exploitation rate of 163%, which led to a generalized drop in the piezometric level in the order of 20 cm/year. This study applied conventional techniques such as hydrochemical compositions, multivariate statistical methods and Geographical Information Systems (GIS). To better identify the processes controlling the hydrogeochemical evolution of groundwater quality of Triassic aquifer and its suitability for drinking uses, 14 well water samples from the Triassic aquifer were analysed for physical character and chemical composition. In the groundwater, the respective order of cation and anion concentration was Na>Ca>Mg>K and SO4>Cl>HCO3. The chemical data of water samples from the study area presented by plotting on a Piper diagram reveals the predominance of two hydrochemical types: a Na-Ca-Mg-SO4 facies and a Na-Ca-Mg-Cl-SO4 facies. Analytical results demonstrate that the chemical composition of groundwater in Triassic aquifer is strongly influenced by residence time and flow path. Water quality deteriorates going from southwest to northeast across the region, coincident with the appearance a clay layer limiting the infiltration of rainwater. The majority of ions are above the maximum desirable limits recommended for drinking water by WHO guidelines and Tunisian Standards (NT.09.14). Based on the Water Quality Index (WQI), 36% of water samples of the Triassic aquifer are classified as "poor water" and they cannot be used for drinking purposes without prior treatment.
Highlights
Tunisia is a country with semi-arid to arid climate over most of its territory
A Triassic aquifer of southeastern Tunisia, which extends over 515 km2, is the major source for fresh water for human consumption and irrigation purposes in the Medenine Governorate
The water samples were analyzed for physicochemical parameters, such as temperature, pH, salinity, Na+, K+, Ca2+, Mg2+, Cl−, F, HCO3−, and SO42−
Summary
Tunisia is a country with semi-arid to arid climate over most of its territory. It is influenced by two very different climates, one Mediterranean to the north and the other Saharan to the south, which causes significant spatial-temporal variation of water resources [1]. Mean annual rainfall is 100 to 230 mm and annual evaporation is1300 to1600 mm [2] In this context, the exploitation of deep aquifers having considerable reserves remains indispensable in order to meet the. A Triassic aquifer of southeastern Tunisia, which extends over 515 km, is the major source for fresh water for human consumption and irrigation purposes in the Medenine Governorate. The surface hydrographical network in the study area is quite dense. Since 1980s, the piezometric level shows an average decline of 0.20 m/year under the effect of the current extraction (Fig. 2)
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