Arsenic speciation and uranium concentrations in drinking water supply wells in Northern Greece: Correlations with redox indicative parameters and implications for groundwater treatment

The cities in the Aksios and Kalikratia areas in Northern Greece rely on arsenic contaminated groundwater for their municipal water supply. As remedial action strongly depends on arsenic speciation, the presence of other possible contaminants, and on the general water composition, a detailed study with samples from 21 representative locations was undertaken. Arsenic concentrations were typically 10–70 μg/L. In the groundwaters of the Aksios area with lower Eh values (87–172 mV), pH 7.5–8.2 and 4–6 mM HCO3 alkalinity, As(III) predominated. Manganese concentrations were mostly above the EC standard of 0.05 mg/L (0.1–0.7 mg/ L). In groundwaters of the Kalikratia area with higher Eh values (272–352 mV), pH 6.7–7.5 and 6–12 mM HCO3 alkalinity, As(V) was the main species. Uranium in the groundwaters was also investigated and correlations with total arsenic concentrations and speciation were examined to understand more of the redox chemistry of the examined groundwaters. Uranium concentrations were in the range 0.01–10 μg/L, with the higher concentrations to occur in the oxidizing groundwaters of the Kalikratia area. Uranium and total arsenic concentrations showed no correlation, whereas uranium concentrations correlated strongly with As(III)/ As(tot) ratios, depicting their use as a possible indicator of groundwater redox conditions. Finally, boron was found to exceed the EC drinking water standard of 1 mg/L in some wells in the Kalikratia area and its removal should also be considered in the design of a remedial action.