Hydrogeochemistry and hydrogeology of a fractured urban aquifer in the metropolitan region of Florianópolis, Southern Brazil

Abstract This paper was carried out through database of hydrogeological information of tubular wells based on the Groundwater Information System (SIAGAS) from the Geological Survey of Brazil (CPRM). The geology of the study area shows two main domains, a complex Crystalline Precambrian Shield partially covered by Quaternary sediments. Two main regional directions of tectonic lineaments were defined using satellite images with NE-SW and NW-SE orientations. The average discharges and specific capacities of the wells show values of 13.1 m 3 /h and 0.59 m 3 /h/m respectively. NW-SE linear structures were more productive than NE-SW, however the highest discharge values and the highest average (15.6 m 3 /h) are related to abstractions influenced by both directions simultaneously. Serra do Tabuleiro Granite is the lithology with the greatest productive potential in the region, followed by São Pedro de Alcântara Granite and the Granite-Gneiss-Migmatitic Complex. Sodium bicarbonate and calcium bicarbonate waters are the two main hydrochemical groups that occur in the region. The dissolution of calcium carbonate filling the fractures of the rocks is the main source responsible for the alkalinity of the water. The cationic proportion is defined by Na + > Ca 2+ > Mg 2+ > K + . In some wells, the increasing of Total Dissolved Solids (TDS) is probably related to the contribution of adjacent Quaternary porous aquifers deposited under marine influence.