Resilience to climate change: adaptation strategies for the water supply system of Formia, Gaeta (Province of Latina, Central Italy)

The aqueduct that serves the municipalities of Formia, Gaeta (province of Latina, Italy), for which “ATO 4” Integrated Urban Water Management Agency is responsible, is supplied by two important karst sources fed by the western Aurunci Mountains: Mazzoccolo spring, with an average flow rate of 1100 l/s, and Capodacqua di Spigno spring, whose average flow rate is 1300 l/s.

Although these sources were already used in ancient Roman times and the quality of their water is excellent, the precipitation regime modifications, caused by climate changes, has exacerbated the following problems:

• a decrease in the flow rates of the springs caused by the cyclical reduction of winter rainfall.
• an increase of turbidity that makes the water temporarily unfit for human consumption.

In order to mitigate these problems affecting a resident population of about 150,000 people, Acqualatina S.p.A. – the water service provider – has promoted a series of unpublished geological, hydrogeological and geophysical studies to increase the knowledge of the hydrogeological aspects and to find additional sources of supply to improve the existing system.

We studied, therefore, a strategy aimed at diversifying the water supply by connecting the adjacent areas to the main water network and by identifying new aquifers in the area that were not affected by the aforementioned problems.

We hereby present the results of the research carried out before and during the construction of the wellfield called "25 Ponti" located in the plain of Formia, in the coastal area near the Tomb of Cicero (Tomba di Cicerone) archaeological site. Four (4) wells with a depth ranging between 55m and 100m and four (4) monitoring piezometers were drilled which intercepted a pressurized aquifer underlying Pleistocene marine terrace deposits, with a thickness ranging between 20m and 75m, which act as an aquiclude. The quality of the water was excellent from a physical chemical and bacteriological point of view, with different chemical properties compared to Mazzoccolo and Capodacqua springs.

The first work carried out during the 2017 water crisis showed an increase in salinity over time, potentially suggesting saltwater intrusion (Sappa, 2019).

In collaboration with D.I.C.E.A., the Department of Civil, Construction and Environmental Engineering of “La Sapienza” University in Rome, the groundwater was monitored to verify, and thus avoid, any saltwater intrusion. To this end, two wells with a total flow rate of about 50 l/s were commissioned and remained active for a period of 8 months (August 2019 - March 2020). About 120 water samples were analyzed from a chemical and isotopic point of view, while the piezometric trend, the electrical conductivity and temperature were recorded by means of multiparameter probes.

The results obtained showed that the increased mineralization of the aquifer follows a seasonal trend regulated by the groundwater extraction from the wells that, in some periods of the year, affects the regulated reserves. This seasonal phenomenon was also confirmed when monitoring was performed in absence of pumping.

To date, the change in salinity is believed to be due to the extraction of deep waters rather than to seawater intrusion.