Conceptual hydrogeologic model of central-western Urucuia aquifer system, Brazil

The Urucuia Aquifer System (UAS) is a set of interrelated aquifers associated with the sedimentary rocks of Urucuia Group. Five geophysical well logs were interpreted and supported the development of conceptual hydrogeologic model. Three electrofacies are identified: (i) regional substrate of Bambuí Group; (ii) eolian system of Posse Formation; (iii) braided fluvial system of Serra das Araras Formation targeted by tabular levels of massive and silicified sandstones. In the hydrogeological context, the stratigraphic position of the silicified sandstones levels in relation to the regional groundwater level leads to the occurrence of unconfined aquifers when it is disposed above, and an aquifer-aquitard-aquifer system when it is located below. In this context, the lower confined aquifer presents hydraulic heads greater than the ones in the overlying unconfined. Silicified sandstones horizons function as aquitards and have become more deep and thick in the central-western portion. Additionally, the effective porosity and storage coefficient values ranging from 10-2 to 10-1 and 10-4, while the transmissivity between 10-6 and 10-4 to 10-3 m2/s for unconfined and confined subtypes, respectively. In the extreme west, the UAS displays wells whose static levels are deep (over 100 m), because of a groundwater divider the hydrogeological basin. In general, the drawdowns produced after the pumping test wells gradually decrease toward SAU western-central portion, combined with an increase of the specific capacity of the wells, the saturated thickness and hydrogeological potential.