Hydro-geochemical Study of the Coastal Aquifer in Tripoli (Lebanon)

Abstract

Groundwater geochemistry refers to the general chemical properties of water, particularly groundwater. Precipitation, volatilization, oxidation/reduction, sorption/partition, and complexation are processes involved in the distribution and fate of organic molecules in water. Determining hydrogeochemical facies is a great help for determining relationships and similarities among the chemistry of waters in an aquifer. This study focused on the coastal aquifer of Tripoli (Lebanon) with Mio-Quaternary age. It is considered as a confined aquifer and an important hydraulic reserve for domestic water use in the region. Recently, it underwent an urban development that leads to an increase in water demand causing a decrease in the piezometric level and a high-risk of deterioration to water quality through seawater intrusion and anthropic pollution. To understand the origin of mineralization and the mechanism of water hydro-chemistry variation and to provide a vision to underground water recharge, this study aims to analyze the hydrodynamic, piezometric, and geochemical characteristics of the coastal aquifer. The fluctuation of physicochemical parameters for cool and warm seasons has been studied and monitored for 16 coastal wells during April, May, and June 2020. Results were interpreted by using a statistical analysis called Principal Components Analysis (PCA). Cartographic of groundwater levels and concentrations for nitrate, chloride, sulphate ions, the ratio sulphate/chloride were determined by using SUFFER8 software. It can be noticed that the Mio-Quaternary formation at Tripoli consists of thick sedimentary sandstones and conglomerates with argillaceous roots, which provide significantly high permeability characteristics. It is mainly recharged from precipitations through karstic formations. Chemical analysis shows that bicarbonate ions (HCO3 -), characterized by dissolution of carbonate rocks from geological upstream formations of Tripoli, means that the aquifer is subjected to intensive recharge of fresh water and snow melting making a hydrostatic equilibrium facing marine intrusion [1]. High contents of chloride and Sodium are due to anthropic contamination or seawater intrusion. However, Magnesium ion concentration assures this intrusion. Meanwhile, nitrates, sulfates and phosphorus high concentrations are related to wastewater leakage or agricultural activities [2].