The groundwater flow system of Terme Alte (Alto Reno Terme, Bologna, Italy)

The thermal field of Porretta Terme, located in the Alto Reno Terme municipality (Bologna), has always raised interest for its peculiar waters since ancient times. Indeed, the use of the springs dates back to the I-II century A.D. and perhaps even in the Etruscan period. Porretta's thermal tradition has developed over the centuries. First regulation, issued in 1936, allowed to cultivate the mineral deposit and its natural gas in a 740 000 acres wide land. The thermal waters, a public good, are indeed ruled by specific laws which control their use through a grant where the Public Authority makes the licensee, usually a private, follow a series of accomplishments aimed at not damaging the quantitative and qualitative characteristics (R.D. July 29, 1927 n. 1443). Fourteen thermo-mineral springs out of the nineteen located in the given land are currently exploited. They are divided into two groups, which differentiate either for the chemical properties of the waters and their topographic location. The first group of springs, called salt-bromoiodic, with higher salinity and temperature, is located in the upper part of Porretta along the Rio Maggiore, a tributary on the left bank of the Reno River. This is the portion of the deposit that has been studied. The second group of springs, called sulphurous, characterized by lower temperatures and salinity, is located south-east Porretta on the left side of the Reno River. These thermo-mineral water resources appear to be very worthy and need particular care and protection. By using the results of past research, the essential bibliography of which has been edited in the end-notes, the aim was to develop the hydrogeological parameters of the aquifer that feeds the thermo-mineral sources, identify and understand the conceptual model of the groundwater circulation system, also detecting the interference between the different sources in the area examined. This type of research, which is usually applied to aquifers in sedimentary and granular soils, can be considered original. Indeed, an exhaustive hydrodynamic parameterization of a fractured thermal aquifer system such as that of Porretta has never been conducted. The collection of observational data on the hydrological regime and on the chemical composition of hot waters during the six months of field surveys, which confirmed the substantial constancy of the values over time, was also remarkable.