Hydrochemical investigation of barium in the public water supply wells of Sao Paulo state, southern Brazil

Barium has frequently been detected in the groundwater of public supply wells in the state of So Paulo (Brazil) at concentrations above the aquifer baseline values and, in some situations, above the potability limit (0.7 mg L-1). In this study, the barium concentration and distribution in the water of 163 supply wells monitored by the state environmental agency have been evaluated, and suggestions to explain its occurrence are also presented. The investigations were of regional to local scale and comprised sampling and chemical analyses of groundwater samples from specific wells and from a pumping test in a well located at the municipality of Galia. The results showed that among all the evaluated aquifers in the state of So Paulo, the greatest number of cases and highest concentrations of barium (1.2 mg L-1) were found in wells that extract water from both the Marilia and Adamantina aquifers (Bauru aquifer system-SAB). The origin of the barium is probably natural and possibly related to the dissolution of the carbonate cement in the Marilia Formation sandstones. Other barium anomalies were observed in the SAB wells that cross both the Adamantina and Santo Anastacio aquifers. In these cases, the barium concentrations show a positive correlation with N-nitrate and chloride, suggesting that the barium anomalies are directly or indirectly related to an anthropic contribution through the infiltration of sewage water from septic systems in the aquifers as recharge.