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FIGURE 12 The distribution of conductivity in the two sectors
of Favignana
FIGURE 11 Ruins of an ancient roof-and-tank set 9125 µS/cm in the well FA04. In the wells of the eastern
sector, values as low as 676 µS/cm and as high as 11110
soon learned to spare it, to manage it without wasting µS/cm (Figure 12) have been measured instead.
it, to secure at least a minimal reserve of water all over Although the mean electrical conductivity values of
the year. Hence, in order to achieve this goal a house the two sectors are not so much different (4359 µS/
building technique has been developed over the cm vs 3563 µS/cm, both high values, anyway, for a
centuries, that allows to collect rain water on the roof groundwater), in the western area a more homogenous
of the houses, from where it is pipe-conveyed down distribution can be observed, while eastwards the
into cisterns often carved out right below the houses values are very different, even at a distance of a few
themselves (Figure 11). hundred meters (Figure 12). This is coherent with the
According to the geographical distribution of the literature, where it is reported that in Favignana two
electrical conductivity values all over the island, two wells can often be found in the very same lot, providing
trends are distinguishable. The electrical conductivity a different kind of water, one fresh and the other salty.
data in the wells of the western sector range (annual This difference mainly depends on the different
average) from 2435 to 4830 µS/cm, with a maximum of geology of the two sectors, as already anticipated above
(Figure 3): in the eastern one, the calcarenite outcrops
are not uniform but commonly alternating with lenses
and thin beds of sands and conglomerates. Therefore
the groundwater in eastern Favignana should be
considered as a set of little aquifers -contiguous and/
or overlapping, isolated or linked together- each with
different water qualities. In the western sector, instead,
outcrops of carbonatic rocks are more abundant with
respect to more scattered calcarenite banks.
26 EAI Energia, Ambiente e Innovazione 4/2015
