Evaluation of the geochemical conditions in the deep aquifer system in Vounargo area (SW Greece) based on hydrochemical data

Abstract

This article investigates the origin and chemical composition of the aquifer hosted in the coastal part near Pyrgos town as well as any possible connection with the tectonic structures of the area. The bedrock in the study area consists of Paleocene limestones of the Ionian zone and evaporites. The post-alpidic sediments consist mainly of clay, marl, siltstone and sandstone. Three major fault trends develop a complex fault system in the wider Pyrgos area. The tectonics and seismicity of the study area are active to date and have played a prominent role in the structure of post-alpidic sediments, the shaping of today’s relief, the development of the drainage network and the local hydrogeological characteristics. Groundwater samples can be classified into two groups based on their water type. The first group corresponds to fresh groundwater of Ca-Mg-HCO₃-(SO₄) type and the second to alkaline waters of Na-(Ca, Mg)-HCO₃-SO₄ type. A number of samples classified into the second group are considered to be modified by rock-water interaction processes. Trace elements exhibit generally low concentrations, while boron concentrations suggest discrimination between the above two water groups. The correlations between different elements and their distribution maps suggest that the main fault of Vounargo provides a preferential path for deep circulation, transmission and mixing of deep and shallow groundwater.