Application of the Discrete Fracture Network method to define the hydrogeological conceptual model of the fractured aquifer in the Jurubatuba region, Sao Paulo, Brazil

This work consisted of a detailed investigation of a fractured crystalline aquifer, with an unconsolidated overburden with a crystalline bedrock from the Embu Complex. The objective was knowing the structural and hydraulic framework for investigating an area contaminated by organochlorine solvents in the Jurubatuba Channel region, in Sao Paulo, Brazil. It is noteworthy that for the first time the Discrete Fracture Network (DFN) method was successfully applied in a tropical region, with detailed data from rock core and geophysical profiling, in addition to the instrumentation used for the measurement of transmissivity and hydraulic loads. . A borehole about 60m deep was drilled, with continuous rock core recovery, described in the field. Geophysical profiling was performed: caliper, natural gamma, acoustic and optical televiewer, temperature (ALS type, brought to Brazil for the first time), as well as hydraulic tests with packer systems. A flexible polyurethane membrane was installed in the open borehole in order to prevent cross-contamination, being removed only for installing the multilevel monitoring system. A Westbay system with 15 monitoring zones was installed, the first of its kind to be installed in Brazil. In another drilling, a CMT type system with 7 monitoring zones was installed. Additionally, in three pre-existing wells, structural data was collected in caliper and acoustic profiles, as well as in hydraulic tests. Outcrops near the boreholes were studied to better understand the fracture framework of the area. It was observed that geological materials previously considered in abrupt contact actually have gradual contacts, with important alternation of materials of different competences and double porosities. In addition, a predominantly downward flow between layers was found, and temperature profiling and packer tests indicated continuity of hydraulic characteristics between different materials. The importance of downward flow is supplanted by horizontal flow from 9.5 to 14.6m, as suggested by strongly depleted oxygen and deuterium isotopic signatures. The portions with higher transmissivities are related to fine gneiss with the fracture sets A (subhorizontal) and B (N064/27, dipping to SE), or the intercalation of fine gneiss, pegmatite and banded gneiss and combination of families A and B, indicating that the flow is not necessarily a function of a single fracture orientation, rather its potential can actually be increased by combining more than one fracture family. Finally, some of the fracture families identified here were also related to structures described in regional works. (AU)