A Preliminary Assessment of Young Water Fractions in Groundwater from Alluvial Aquifers Facing the Northern Italian Apennines

This study sums up the first estimates of the young water fraction (Fyw; here understood
as the percentage proportion of groundwater passing through the well’s screen and younger than
approximately 2–3 months) from groundwater collected in 75 wells from alluvial fans facing the
northern Italian Apennines of Italy. The Fyw estimates were based on a monthly dataset of waterstable
isotopes (oxygen-18 (18O)) from surficial water (9 rivers), while the dataset of groundwater
(75 wells) consisted of three-monthly isotopic data. In the cases of surficial water and stable isotopes,
these lasted over the period of January 2003 to December 2007, while in the case of groundwater,
the data were collected from January 2005 to December 2007. The values of Fyw were estimated
by means of a sine-wave fitting technique; the results made evident the presence of unexpectedly
reduced differences between groundwater. In particular, shallower groundwater hosted in aquifers
from the apical parts of the alluvial fans (i.e., aquifers characterized by the coarsest materials such
as gravels and sands, and closest to the recharge areas) showed similar values of Fyw to the deepest
aquifers from the distal parts; however, former studies mentioned here evidenced the existence of
poorly recharged old groundwater. Our results seem to confirm a complex behavior of these aquifers
compared with what had previously been thought.