1. a Campania Speleological Federation , Caserta , Italy
2. b Research Institute for Geo-Hydrologic Protection , National Research Council , Cosenza , Italy
3. c Research Institute for Geo-Hydrologic Protection , National Research Council , Via Amendola 122-I, 70126 , Bari , Italy
4. d Dept. Hydraulic, Geotechnical and Environmental Engineering , University “Federico II” , Naples , Italy