Hydraulic interactions between aquifers in the Viterbo area (Central Italy)
Urban Groundwater, Meeting the Challenge
The Regione Lazio-Direzione Regionale dello Sviluppo Economico e delle Attività Produttive (RL-DRSEAP), carrying out its public functions to govern the use of mineral resources (including thermal water), planned the exploitation of the Viterbo hydrothermal system on the basis of a conceptual hydrogeological model (CHM). The CHMs of the Viterbo area and that of the neighboring Tuscany region, characterized by the same geological and hydrogeological setting, are discussed, suggesting the
... esting the unreliability of the CHM model. Methods: Research for the CHM for the Viterbo hydrothermal system was carried out on the basis of geological and hydrogeological surveys at a scale of 1:10,000. The equipotential level and temperature of 70 wells was checked and the yield and temperature of 14 springs (10 of thermal water and 4 of cold water) was measured by the volumetric method and use of a digital thermometer in 2017, while the yield of the Bullicame spring has been monitored by the Municipality of Viterbo since March 2001 using an ultrasonic instrument. Results: The proposed alternative CHM shows that the Viterbo hydrothermal system is experiencing a continuous hydric crisis. This is documented by the decreasing residual yield of springs, boreholes, and wells of thermal water over the last 162 years, due to natural JEPT factors and the indiscriminate drilling of many wells over the last 67 years. At present the total yield is 61 L/s, i.e. the maximum sustainable yield, and it is very likely that this yield will continue to decrease in the future. Conclusions: The RL -DRSEAP should avoid using the unreliable CHM for the exploitation of geothermal resources. High resolution reflection seismic prospecting, seismic and geo electric tomography, and the radionuclides of the noble gases 39 Ar, 81 Kr, and 85 Kr could be useful to check the proposed alternative CHM.