Factor Analysis in the Study of Geochemical Processes in the Apodi Sedimentary Basin, Northeast of Brazil

Wells of the Jandaira aquifer (in the Northeast of Brazil) were sampled for analyses of Ca2+, Mg2+, Na+, K+, Cl-, SO4 2-, HCO3 -, CO3 2-, NH4 +, NO2 -, NO3 - , Fe, pH, hardness, and electric conductivity (EC). 87 wells were sampled during the dry season of 2009 and during the rainy season of 2010. R-mode factor analysis was applied, using WINSTAT software and the centroid method and Varimax rotation, for the identification of interrelations between the parameters studied. Variables that contribute significantly to the principal factor during both dry and rainy season are Cl-, EC, hardness, Na+ and Mg2+; K+ plays a role during the dry season only and CO3 2- during the rainy season. It is seen that, in general, recharge to the aquifer reduces the load of the two principal factors in favor of the others. R-mode factor analysis emphasizes the seasonal changes that occur, even when they are too small to be detected in the individual results of chemical analyses on the large compound of samples.