Differentiation between alluvial and deep aquifer waters in the townships of Crato and Juazeiro do Norte, Ceara State, Brazil

We studied a group of deep-wells in the townships of Crato and Juazeiro do Norte, in the Cariri region, in the South of Ceara State. In this region, which is of high economic importance for the State, exclusively underground-water is used for public water supplies. Hydrogeologic conditions are complicated and deep wells produce waters of mixed origin which are difficult to be characterized. Using carbon-14 concentrations (expressed in pMC) and electric conductivity (CE, measured in μS/cm) we can distinguish alluvial waters from those originating from deeper aquifers (Rio da Batateira e Missao Velha). Alluvial waters exhibit a positive correlation between CE and pMC. For Crato, CE=30.3 pMC - 3185 (R=0.996) with pMC higher than 100 and CE ranging from 88 to 497 μS/cm was obtained, Juazeiro do Norte wells gave CE = 0.98 pMC + 100.31 (R=0.84), with pMC from 66.6 to 124.8 and CE from 162 and 226 μS/cm. Deep aquifer samples show a negative correlation between CE and pMC. (author)