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 underground waters of the island vary greatly and are generally
characterised by: temperatures included 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 potassic volcanic rocks. Four water
groups were recognised: bicarbonate-calcic; bicarbonate-alkaline;
transition; sulphate-chloride-alkaline, directly connectable to the
geological-volcanic model of the Island.