Hydrochemistry of an aquifer in Quaternary loess like sediments in the Pampean Plain, Argentina

Abstract

Loess like sediments cover an area of about 1.800.000 km2 in the Pampa plain of Argentina, forming an aquifer system which is used for water supply for most of the cities an rural population in the region. This aquifer supplies water to agricultural productive activities that contribute to about a 60% of the national gross produce of the country. In this paper, detailed studies in a local sector of the aquifer near to Mar del Plata, in the landÆ lling area of the city, are performed. The main goal is to characterise the hydrogeochemical processes giving the chemical groundwater composition, and to analyze the impact of the inÆ ltration of the leachate from a neighbouring landÆ ll on some samples. Five wells were drilled to take sediments and water samples. The textural and mineralogical composition of the aquifer sediments was analysed and the chemical composition of groundwater was determined. The equilibrium relationship between the solid phase and groundwater was considered using speciÆ c computer codes. The achieved conclusions were that the chemical composition of groundwater is mainly due to calcite equilibrium and cationic exchange with calcium uptake and sodium release. The dissolution of amorphous silica minerals, and subordinate silicate hydrolysis, are responsible of the characteristic high dissolved silica concentrations. High chloride and nitrate contents result from leachate infiltration, but the main geochemical processes in the mix are the same.