Lombardi Research Group - The San Vittorino Valley
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The San Vittorino Valley

The San Vittorino Valley

The San Vittorino valley is an agricultural intramontane basin that is filled with up to 170 m of river and lake sediments. 

Faults not only border the plain, but also cross it and deform the plastic sediments. Large volumes of CO2 migrate along these faults and are released at the surface, both from gas vents and from bubbling mineralised springs.

More than 30 sinkholes exist throughout the valley; many of these are water filled and have gas bubbling inside of them, and thus it is likely that they were formed by groundwater acidification by deep CO2 and subsequent alteration of the carbonate rich sediments. Some of these bubbling sinkholes even occur within a small town, while another is exploited for a thermal bath and health spa.

This site is considered unique for many reasons, including:

- it is a CO2 leaking site that is not in a volcanic/geothermal area;

- gas is leaking along faults occurring in plastic sediments;

- some of the leaks are occurring in populated areas and have even been commercially exploited;

- sinkholes have formed and groundwater chemistry has changed as a result of the leaking gas;

- there is evidence that some leaks have stopped due to self-sealing processes.

We first started research in the San Vittorino valley in 2000, when we received funding from the Region of Lazio to study the link between hydrogeology, deep gases, and sinkhole formation.

During this project we conducted an extensive soil gas survey of the entire valley and were able to identify a number of inferred faults on the valley floor that are difficult to identify using classical techniques due to the plastic nature of the local sediments.  The deep-origin gases of helium and CO2 were found to be particularly useful in this regard.

At the same time we also collected water samples from a large number of the sinkholes, bubbling pools, springs, and wells that occur throughout the valley, and performed a complete suite of analyses for dissolved elements and gases.  This work defined three different water types in the valley, one being highly mineralised and associated with gas emanations, elevated soil gas anomalies, and sinkholes. 

A subsequent project from the Region of Lazio involved the development of an autonomous geochemical / geophysical station to monitor for the potential connection between earthquake activity and dissolved CO2 concentration in groundwater.  This monitoring station was built by our group using both in-house and commercially available parts (combining geophones and a gas-permeable sampling membrane in one observational well), and collected data for almost one complete year

Our research continued within EC funded Nascent project. Of particular interest for this project was the need understand the possible impact on groundwater quality should CO2 leak from a geological storage reservoir.  Additional sampling for both soil gas and groundwater was conducted in this project to add to the database already collected during our previous studies.  Results showed that despite the extreme conditions of this site (i.e. very large volumes of CO2 leaking for hundreds, maybe thousands of years) groundwater quality still remained within drinking water limits. This project also allowed us to continue the operation of the installed monitoring station, and to continue its development and improvement.

Most recently we have studied the potential impact of CO2 leakage on groundwater quality within the RISCS project. This work involved drilling shallow wells up-gradient, within, and down-gradient of a CObubbling sinkhole and collecting groundwater samples for the analysis of major and trace elements.

Compared to similar work that we performed at the silicate-rich Latera site, the data from the San Vittorino site instead showed the importance of the local carbonate-rich rocks and soil to buffer the COinduced acidity and minimise impacts.