HYDROGEOLOGY OF BRASÍLIA (DF) SOBRADINHO RIVER BASIN
José Luiz G. Zoby and Uriel Duarte
Instituto de Geociências, Universidade de São Paulo.
Presented by IGOR G. PACCA
The Sobradinho river basin is located in the center-north portion of the Distrito Federal and comprises an area of 144 km2. At least 22,500 persons depend exclusively on the groundwater. The studied area is geologically composed by metasedimentary rocks of proterozoic age covered by a thick weathering mantle. Two aquifer domains were individualized in the hydrogeological context, which are the Porous Domain and the Fractured Domain. The Fractured Domain was classified in two systems named Paranoá and Canastra. The Paranoá System was subdivided in four aquifer systems: Sandy Metarythmite (mean yield 26.7 m3/h), Quartzite (mean yield 8.7 m3/h), Clayey Metarythmite (mean yield 4.6 m3/h) and Psamitic-Pelitic Carbonated (mean yield 15.7 m3/h). As there were no wells in the Canastra System it remained individed. The main producing fractures in the wells are concentrated until the 100m deepness. The Porous Domain is represented by the weathering mantle (soil and weathered rock), which achieves more than 100m thickness, and is associated to unconfined aquifers with great lateral continuity. The thickness and permeability of the weathering mantle are strongly influenced by the geological basement. The Porous Domain is exploited by excavated wells. The mean annual rainfall in the area is of 1,442.5mm. Approximately 28% of the rainfall takes part in the aquifer recharge. The main groundwater use is domestic. The waters have good physical-chemical quality. Bacteriological contamination in water samples from the weathering mantle is related to the technical constructive deficiencies of the excavated wells and the nearness between cesspit and well. Technical constructive problems with sanitary protection and procedures of unactivation and abandonment of the deep groundwater wells were recognized.
( November 19, 1999 ) .
Publication Dates
-
Publication in this collection
07 Aug 2000 -
Date of issue
June 2000
