Considerations About Deep Hydraulic Connection Of An Unconfined Aquifer In Fault Zones From Isotopic Data, Ne/Brazil

The Barreiras Aquifer has a majorly unconfined character, and is particularly affected by the geological structures in the coastal strip of northeastern Brazil. Its hydrogeological substrate is represented by a carbonate sequence of Mesozoic age, which presents characteristics of aquitard in its upper portion. In this context, the occurrence of bicarbonate waters in the Barreiras Aquifer, to the detriment of sodium chlorinated waters typical of this source, are credited to interactions with the top of the carbonatic aquitard, either in the form of dissolution or in the form of upward vertical drainage, both in the next to faults zones. In the present study, the objective was to contribute to tha analysis of the impact of this regional structuring on hydraulic connections, especially those of a deeper character between the Mesozoic and Cenozoic contexts, which would also be providing water mixtures within the Barreiras Aquifer. The methodology was based on the analysis of environmental isotopes delta O-1(8) and delta H-2 and overlapping of this information with the previously characterized regional structuring context. Preliminary results reveal isotopic signatures characteristic of Mesozoic source in samples obtained from wells in the Barreiras Aquifer, particularly next to deep regional faults. This hydraulic connection would be increased by the transtensional character of these faults, which can act as pressure relief zones in the subsurface.