Hydrogeological and hydrochemical characterization of unconfined aquifer located in the alteration mantle of the Serra Geral Formation, in the Taquari-Antas river basin, northeast of Rio Grande do Sul State

This paper presents the hydrogeological and hydrochemical characterization of the unconfined aquifer located in the alteration mantle in the volcanic rocks from Serra Geral Formation, in the northeast region of Rio Grande do Sul State. This aquifer is conditioned by the soil, topography, lithology and climate, being characterized by a saturated layer thinner than 1,7 m, static levels between 0 and 1 m and low flow (<0,5 m3/h). These waters are of calcium or magnesium bicarbonate type, and low alkalinity and electrical conductivity, low calcium, magnesium, sodium, potassium and chloride concentrations, and high iron and manganese concentrations. Additionally, these waters have high concentration of nitrates (mean above 10 mg/L) and the presence of total coliforms. These characteristics evidence a quick circulation between the recharging and discharge zones in the aquifer.