Location of recharge area of Gorgovivo Spring, Central Italy. A contribution from isotope hydrology

The present study deals with the problem of characterization of the recharge zone and the mechanisms of water renewal at the Gorgovivo spring, which feeds the aqueduct of the Ancona province. For achieving with precision the hydrogeological and geochemical dynamics, analyses of chemical, isotopic and tritium contents have been used. The presence of different meteorological stations to measure of rainfall amount and isotopic contents in precipitation has allowed to evaluate the altitude gradient which correlates the oxygen-18 content in the underground waters with the isotopic height of infiltration. This gradients (about -0.24% per mille 100 m) allowed to establish around 1400 m as the intake altitude for Gorgovivo spring. Tritium contents (about 8-13 TU for shallow springs present in the area, 6-8 TU for Gorgovivo spring) and the different isotopic composition indicate the presence in groundwater of a double flowpath. The first one is shallow and very fast: to this pathway belong the ooze springs in the studied area. The second pathway is slow and deeper. It readies the bottom part of bedrock (Massive Limestone). As result, the groundwater recharging Gorgovivo spring can be considered as a mixing between these two pathways. The liquid discharge of the spring is exceptional, thus Gorgovivo spring is one among the greatest Apennine springs both in terms of importance and quality.The stable isotopic composition and tritium contents have allowed to investigate the recharge area and the mechanisms of recharge of such spring. (author)