Geochemical analysis of groundwater in Fortaleza, Ceará – Brasil

Abstract

This research address a geochemical analysis groundwater in Fortaleza, Ceará, Brasil, showing the correlation between the various chemical types and lithotypes of area.  Were used 291 samples collected in the period from 2001 to 2011 for physical and chemical analyzes. There is a predominance of Sodic chlorinated waters, resulting from the relative rNa> rMg> rCa and rCl> HCO₃> rSO₄.  The pH in the waters are predominantly acidic, probably associated with the geological environment (Barriers) and the rainfall recharge. The nitrate grows toward northwest-north, reflecting (probably) the effect of anthropogenic actions caused by concentration of the population in the districts João Arruda (sector northwest) and Cristo Redentor (northern sector). The amount of chlorides and STD increase punctually at northern portion (Neighborhood Cristo Redentor and Pirambu), northwest (Neighborhood Dionísio Torres) and the south (Neighborhoods Passaré and Barroso), during the rainy season, and southwest (Neighborhoods Parangaba and Bom Jardim) during the dry season, which can be produced by several factors, and the more likely the dissolution and the evaporation process. In the first case, the concentration by dissolution in groundwater tends to achieve a balance with the rocks that are in contact, and the slower the movement is greater than the time of contact, therefore, the greater will be the increase in total concentration of salts in the water of the aquifer; the second process is influenced mainly by the weather, it can check the appearance of higher concentrations of salts in the regions of hot and dry climates. From ionic relations of groundwater, it can be seen that rMg⁺² /rCa⁺² with predominance of values greater than 1.258 meq/L (63%), indicating the association of silicates magnesianos present in lithotypes of area. The relation rK⁺/rNa⁺ showed values between 0.009 and 0.840 meq/L, principally resulting from the setting of K⁺ in clay minerals. The waters of Fortress are predominantly Chlorinated and Sodic, independent of the sampling period.