The Apulian carbonate rocks, that constitute the largest coastal aquifer in the region, often include varying amounts of a residual product of weathering known as ''terra rossa''. ''Terra rossa'' is widely and variously distributed and, being rich in Ra-226, labels the water of this karst aquifer with Rn-222 concentrations ranging from a few dozen pCi/l to over 10,000 pCi/l. Such natural labelling provides a good tracer for studies in hydrogeology as it does not only help detecting for conditions of permeability of the water-bearing system but also outlines the main water circuits. Ground water now is naturally affected by such factors as periodic and non-periodic sea level variations, in addition to the processes of groundwater supply and depletion. These phenomena are enhanced, often quite heavly, by pumping water for the various branches of human activity as a result of which groundwater flows with velocity gradients and along directions that may be quite different from those of naturally flowing water. Many water points were surveyed: it was found that, although water is withdrawn at regular intrvals, Rn-222 concentrations often show a pulsatile behaviour due to the fact that water is drawn from different pervious levels that contribute to supply the required discharge in various proportions.
