Groundwater chemistry and arsenic occurrence in the phreatic aquifer system of the San Vitale Pine Forest

The groundwater of the San Vitale Pine forest in Ravenna (Italy), are severely affected by coastal saline intrusion. Sixteen piezometers were sampled at various depths in order to understand the dynamics of groundwater chemistry occurring close to the freshwater/saline interface. A staddle packer was applied to recover 3 to 4 samples from the upper aquifer in each piezometer, sampling the top, the bottom of the upper aquifer (ca. 10 m) and some sample above and below the saline interface. Major chemical composition and selected trace elements were investigated in this study and were used to characterize the hydrogeochemical features of the phreatic aquifer in the area. Also arsenic was determined, and the results show total arsenic concentrations in the range of 0.6 to 92 μg/l, the average being 26.6 μg/l. About 60% of these wells reached arsenic concentrations which exceeded the current Italian legal maximum contaminant level of 10 μg/l. The maximum amounts of dissolved arsenic in the groundwater are related to the sample above the saline interface. The concentration profile correlates positively to Fe2+, and negatively to S2‐ and Eh, according to the characteristics of a strongly reducing aquifer derived from alluvium. The occurrence of high As contents in the upper aquifer is a new finding that stimulates further research on the subject.