Exploratory data analysis of electric conductivity of water in the Serra Geral aquifer system in the Rio Grande do Sul end Santa Catarina States, Brazil

Abstract

The Exploratory Data Analysis (EDA) technique applied to electrical conductivity field measures in 7,620 groundwater samples of the Serra Geral aquifer system in Rio Grande do Sul and Santa Catarina States has revealed four distinct classes. The values above 378.35 μS/cm were considered anomalous and represent the C1 class. Electrical conductivities between 117.35 and 378.35 μS/cm are background values. A physical-chemical analysis conducted at 356 well water samples across the various classes determined by exploratory analysis has shown different hydrochemical evolution paths within the Serra Geral Aquifer System. The class bearing the higher values of electrical conductivity represents the oldest waters with strong relationship with regional structures, such as fault zones and large lineaments. Locally there are mixture through ascending recharge with water from porous aquifers (Guarani Aquifer System and Permian aquifers). The C2 and C3 classes are considered to be the typical water for this aquifer system and slight variations are probably due to the different residence times. Water samples belonging to the C4 class represent younger waters recently infiltrated by the meteoric recharge through the weathering zone of volcanic rocks.