During the ten-year period from 1988 to1998, 83 thermal establishments located near springs and wells that are important to the reconstruction of the water circulation plan were monitored. The samples were drawn periodically in the communes of Casamicciola (22 thermal establishments), Ischia (28 thermal establishments), Forio (17 thermal establishments), Serrara Fontana (7 thermal establishments), Lacco Ameno (7 thermal establishments) and Barano (2 thermal establishments).
The analysis concerned the determination of the main chemical-physical parameters (temperature, pH and electric conductibility) and that of a large series of anions and cations.
The concentration of cations was determined through a spectrophotometry of atomic absorption, that of the anions through ionic chromatography and that of the silica through the colorimetric method. It was found that the subterranean waters of the island vary greatly and are generally characterised by: temperatures between 18 and 90°C; an electric conductibility between 841 and 56000 mS/cm; high levels of alkali and silica (up to about 600mg/l), the latter being typical of subterranean water circuits in volcanic potassium rocks.
Four water groups were recognised: bicarbonate-calcium; bicarbonate- alkaline; transitional waters; sulphate- chlorate-alkaline,
directly connectable to the geological-volcanic model of the Island.
