A total of 53 points has been selected to measure radon concentrations
(42 private and public wells and 11 springs). These
points correspond to different aquifer systems (Fig. 1). Two samplings
have been carried out in 2007. In the first one [May 7 to
September 13] a total of 23 wells and 9 springs of alluvial-volcanic
aquifers were measured. In the second one [October 22 to
November 24] the same wells and springs were measured but two
(12 and 25); one because of being dry and the second because
became inaccessible. In addition, we expanded the sampling with
21 alluvial aquifer points. Wherever the radon levels obtained in
both samplings differed by more than 50% and at least one was
higher than the whole survey average, an additional measurement
was taken one month later. In springs we took water directly from
the source, whereas in wells we had to use different water pumps
for sampling from 1 m under water level to avoid superficial and
stagnant waters. 250 ml glass bottles were used to avoid radon
leakage during transport to our laboratory. Using a flow cell and a