Inorganic parameters as water quality indicators in acidic groundwater in a Tropical Region - Brasilia-DF (Brazil)

In Brazilian Tropical Cerrado Region, reactions related to parental-material breakdown and oxisols genesis strongly affect the groundwater chemical characteristics. These reactions are responsible for the low water pH values, the soil charge balance, and the re-equilibrium of dissolved inorganic carbon species. Brasilia, the capital of Brazil, lies in the Distrito Federal, in the central part of the Brazilian Cerrado Region and has been experiencing an intense urban development during the last 15 years. Many town-house complexes have been built without proper water supply or wastewater disposal conditions. In this work, we discuss the adequacy of traditional ground waters geochemical classification models applied to the most exploited aquifers in DF. Forty groundwater samples were collected and pH, conductivity and total dissolved solids were determined in the field. Na, K, Ca, Mg, Fe, Al, Cu, Cd, Cr, Mn e Zn were determined by Inductively Coupled Plasma Atomic Emission Spectrometry and Atomic Absorption Spectrophotometry. We identify inorganic indicators of human interference on the quality of these waters and also suggest a new mean of interpretation of dissolved inorganic elements based on statistic treatment of multivariate data. It is revealed a particular geochemical feature concerning to the alkali and the earth alkali metals concentrations, and a typical trace-element behaviour, closely related to the human activities and to the geological-bearing material characteristics. For all of the samples supposed to be altered by any kind of human activity, the physico-chemical parameters were lower than the standards established by the water quality legal system.