Contamination saline dans les eaux souterraines de la plaine d'Akkar au Liban

Saline contamination in groundwater of Akkar plain in Lebanon

¹ Université Libanaise. Faculté de Santé Publique, Section 3, B. P. 246, Tripoli, Liban
² Université des Sciences et Technologies de Lille. Laboratoire de Chimie Analytique et Marine, (UPRESA CNRS 8013, FR CNRS 1818), Bâtiment C8 - 59655 Villeneuve d'Ascq Cedex, France
³ Professeur émérite à l'Université d'Artois, membre du Conseil Supérieur d'Hygiène Publique de France

Résumé

La salinité des eaux souterraines de la partie nord-ouest de la plaine d'Akkar au Liban du Nord constitue un aspect de la dégradation de la qualité des eaux utilisées dans la consommation humaine et en irrigation. Cette contamination vient s'ajouter à la pollution microbiologique et à la teneur excessive des nitrates dépassant les seuils autorisés. Afin de déterminer l'ampleur de cette intrusion saline, les raisons de cette contamination dans la nappe alluviale de cette plaine côtière et les solutions possibles pour mettre fin à cette situation, la conductivité électrique de 94 puits de cette plaine a été suivie durant quatre années consécutives (de 1997 à 2000), 46 échantillons ont subi des analyses chimiques approfondies. Les valeurs obtenues ont été utilisées pour identifier les villages atteints et ont permis une zonation hydrogéochimique de l'aquifère de la plaine côtière en fonction de différents types d'eaux. L'évolution de la conductivité durant ces quatre dernières années montre une tendance à la croissance de la salinité dans les eaux souterraines mettant en danger l'agriculture, l'économie de la région et la santé des habitants. Les raisons de cette salinité seraient dues à la non conformité des salines du village de Cheikh Zennad, au pompage intensif des puits de la région, à l'excavation du sable et des cailloux le long de la côte de Cheikh Zennad et au déversement spontané des eaux thermales d'Es-Sammaqyé dans les champs. Des solutions sont proposées pour faire face aux besoins croissants de la région en eau et pour retrouver une meilleure qualité de la nappe côtière.

Abstract

The Akkar plain is situated in the north of Lebanon, its surface area is about 110 km², and approximately 130000 people lived in this region. It is the second agricultural area and the largest coastal plain of Lebanon. The coastal plain is undulating, mixed fluvial and marine Quaternary deposits, mostly in the north, while Neogene marly limestones are more dominant in the south.

The inhabitants of the area live under deplorable hygiène conditions due to their poverty and the lack of both medical care and medical prevention centers. Moreover, there is no public networks of sewers and drinking water. Population, industries and farmers use private wells for their daily requirements of waters. Wastewaters are discharged directly in the environment without proper treatment.

A water quality study performed since 1997 reveals a significant microbiological pollution, a very serious contamination by nitrates, and an excess salinity problem. Since the eighties, the population started to live with saline water without any intervention of the public authorities. The inhabitants continued to consume brackish water without realizing the impending medical risks and despite of the occurrence of gastro-enteric diseases and cardiovascular disorders.

The study on the origin and the evolution of saline contamination were conducted during the period of 1997-2000. Ninety four accessible private wells covering the entire area were monitored with conductivity measurements and Chemical analyses. This survey is used to locate primary sources of salinity contamination in the coastal aquifer. The results allowed a hydrogeochemical zonation of the aquifer, based on the presence of various types of water. The evolution of conductivity during the last four years showed an increase in the groundwater salinity.

The saline intrusion noted in the coastal aquifer is mainly due to four factors:

1 - The non-conformity of the sait marshes at the entry of the village of Sheikh Zennad. Two years after the construction of thèse salines in 1968, salted water have been stated by the population.

2 - The coastal aquifer of the plain was overexploited during the last years to ensure an agricultural activity in the area. This overexploitation generated the development of several depression to more than 30 meters under the sea level.

3 - In the absence of public authorities during the civil war (1976-1992), people excavated illegally sand and stones along the coast of Sheikh Zennad village. The excavated shoreline extends on 2 km length and 500 m width. This artificial modification of the shoreline increased by about 500 m of natural interface between fresh water and seawater.

4 - In 1965, an artesian well to approximately 650 m depth was done in Es- Sammaqiye village. At 575 m depth, a brackish hot sulphur water spouts out spontaneously with a flow of 60 litres/seconde. A spa center was built in Al-Arida village on the littoral located at approximately 3 km from the well. With the beginning of the tragic events in 1975, the project was stopped and the well was condemned. But, water continue to leak at several places along the pipe especially in Es-Sammaqiye village. This brackish water undoubtedly reached the water table and contribute to increase its salinity.

The use of brackish groundwater for both agricultural needs and human consumption is not recommended, so it is urgent to find a solution to this problem.

To stop the harmful consequences of saline water consumption, some decisions must be taken rapidly, such as:

• prohibition of non-conform salines in the area;

• construction of water supply networks in the plain;

• creation of a hydraulic barrier at the seawater and fresh water interface.

This can be created by fresh water injection (artificial recharge);

• monitor the water quality and the evolution of the hydrological parameters;

• management of groundwater exploitation;

• declare a moratorium on the exploitation of ail wells during at least 5 years to allow the return to a better quality of the groundwater in the coastal aquifer.