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Hydrology and quality of the Grombalia groundwater table (North‐East Tunisia) Volume 15, issue 2, AVRIL-MAI-JUIN

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Authors
Laboratoire de ressources minérales et environnement, Département de géologie, Faculté des sciences de Tunis, Campus universitaire 1060 Tunis, Tunisie <Abdelazizsebeiyahoo.fr>

The study area which is located about forty kilometres South of Tunis, is an ancient bay widely open onto the Northwest and communicating with the Bay of Tunis. It is a plain which belongs to a multilayer, three‐level groundwater system composed of a phreatic table, a semi‐deep table and a deep table, the whole of which covers an area of 719 km 2, out of which 407 km 2 belong to the Quaternary period. The geochemical study of the water of the phreatic table which took place during two periods (May 2000 and April 2001) was performed by measuring the physico‐chemical parameters in situ, and by analysing the major elements (anions and cations) as well as the nutrients in the laboratory. It showed that the underground waters are characterised by a salinity ranging from 0.7 g\L and 4.7 g\L and that the concentration of the major ions, which was generally above the national and international norms, indicates a gradient increasing from the upstream to the downstream part of the plain. The analysis of the nutriments revealed that the ammonium and nitrite contents were generally below the nationals norms, while the nitrate presents a high concentration in the downstream part, which indicates a contamination of the table at this level. The relatively high nitrate contents, especially in the downstream part of the plain can be due to the leaching of farmlands containing fertilisers, to industrial discharges, as well as to the decomposition of organic matter.