The following paper reports the preliminary results of isotopic analyses that have been carried out on the basis
of 55 water-wells of the alluvial Friuli Plain. Most wells are located in the Low Plain between the spring and the coast lines,
where a multistrata aquifer system characterizes the underground environment. One well is located in the High Plain,
bounded by the Tagliamento moraines to the N and the spring line to the S; it reaches the unconfined aquifer system
continuously developing in the highly pervious alluvial sediments of the sector. Hydrogen and oxygen isotopic composition
of the waters (sampled in April 2003 – April 2006 – July 2006 – October 2006 – March 2007) are shown and compared to
the ones coming from 17 sampling points of surfacing spring waters and to the weighted mean composition of the
precipitations registered in some stations of the area (Trieste, Basovizza, Udine and Rivo). The outcoming distribution of
the above-mentioned isotopes related with the Northern Italy Meteoric Water Line (MWL_S) and the Global Meteoric
Water Line (GMWL) supports the meteoric origin of the studied groundwaters. The involvement of precipitations occurring
at higher altitude and/or at lower temperature in past ages is pointed out. Radiocarbon data, related to three water samples of
the deepest Aquifer H (more than -300 m b.s.l.), are also reported and discussed.
