Influencias Geológicas y Antrópicas en la Calidad de las Aguas Subterráneas Localizadas al Sur de Brasilia (DF), Brasil

Abstract

This study aims to evaluate the effects of geological and anthropogenic processes on the quality of the groundwater from southern Brasilia, Brazil. The studied area is situated in the Brasilia Fold Belt where distinct lithologies from Paranoa and Canastra groups, Cenozoic soils and alluviums are found. Samples were collected at wells located at the different geological units and superposed by contrasting soils types used for human settlement and agricultural purposes. Major ions and physical- chemical parameters were interpreted through multivariate statistical techniques. Our data show that the studied waters have distinct compositions which are mainly connected with: (1) carbonate dissolution; (2) percolation of sewage disposed in non-septic tanks; (3) infiltration of small soil particles into the groundwater due to constructive problems of the wells; and (4) groundwater acidification due to leaching of extremely weathered soils and parental material being naturally low in alkali earth elements. The soil textures have serious implications for groundwater protection from sewage percolation. The groundwater located below coursed fraction ferrasols is at risk of contamination by nitrogen compounds from untreated sewage, which may contribute to groundwater acidification through nitrification. All parameters analyzed are mainly associated with unique sources, where geological and pedological features control the chemical composition of the groundwater.