GHGT-16 site visit to Limagne D’Allier Basin ‘Natural CO2 release’ – 28th October 2022


By Nicola Clarke

4 November 2022

Following the 16th Greenhouse Gas Control Technologies Conference (GHGT-16) in Lyon, France two parallel site visits were organised by BRGM and IFPEN. The first was to the Limagne d’Allier basin, close to Clermont-Ferrand where natural CO2 migration through faults into rivers and groundwaters as well as impacts on the local environment was observed. The second site visits were to CO2 capture test facilities in IFPEN complex in Lyon and the CimentAlgue project (VICAT) in Montalieu-Vercieu (covered in a separate blog post).

On the drive to the CO2 release site we passed through part of the French Massif Central, one of the largest areas of crystalline basement outcrops in France. The day was organised into three parts: a visit to the Saladis springs, a tour of the Sainte Marguerite carbonated water factory and a visit to the Sainte Marguerite site (an old spa hotel and grounds).

The Saladis springs are located on elevated river terraces of the Allier river, a tributary of the Loire, on the inside of a wide meander. Within view are Tertiary sedimentary basin fill of the Limagne d’Allier graben and in the middle distance are outcropping volcanic edifices and flows. Three levels of alluvial terraces are visible and are impregnated with travertine (a textured limestone rock formed around mineral springs) which has allowed for dating of the terraces (~250,000 yrs, ~135,000 yrs and 8,000 yrs).

Two points of interest were visited, firstly the main springs where mineralised and CO2 rich water is entering a small pond via a fault network (see photo). The springs are of sodium-bicarbonate (Na-HCO3) and contain significant chloride (Cl). Mineralisation and precipitation of travertine is common. The gas emitted is nearly pure CO2 with trace amounts of helium. These springs are cold and slightly acidic. Secondly, not far from the springs are some salt meadows where mineralised and CO2 rich water rises in a diffuse manner and are habited with halophilic flora (salt tolerant) more commonly associated with coastal areas.

After enjoying views of the river and surrounding area we took a short drive to the Sainte Marguerite mineral water bottling factory which bottles more than 17 million litres per year. After an informative tour of the facilities, where we observed the full bottling procedure, we were able to sample the water for ourselves before walking across the road to the last stop for the day. The Sainte Marguerite site comprises an abandoned spa hotel and grounds which are located on the flood plain and in its heyday in the 18th century had at least nine springs, many of which are now abandoned. In 1840 the spa included nine baths and offered a variety of treatments, however, it now lies in ruins due to the tendency to flooding. The first bottled water marketed as medicinal water went to market in 1929.

Three springs are left flowing freely on site, the first to be visited was the ‘Brissac’ spring which flows as a small geyser in 20 minute intervals with water emerging from a small pipe into a pond. This repeated action impacts the water with amongst other things an: increase in temperature; decrease in pH; and decrease in dissolved oxygen (redox value Eh). A second spring, the Tennis spring, is rich in CO2 and the hottest at 30°C at the surface. Highly mineralised it is characterised by an array of natural colours and the formation of travertine deposits which radiate from the springs like small deltas. Red (iron oxides) and black (algae) colours are common and halophilic flora colonises the area.

The gas phase associated with the mineral waters is almost pure CO2 with trace amounts of methane and other atmospheric gases. The team from BGRM demonstrated a variety of surface monitoring techniques: pH monitoring; soil CO2 flux monitoring using the chamber method (see photo); and soil gas monitoring using a probe insertion and infrared gas analyser. Striking results from the flux monitoring showed CO2 flux of around 0.5% yet when the soil gas was measured by the probe at 1 meter depths the CO2 was almost 100%. Lively discussions and interactions were made by the 30 delegates on the trip and we were well looked after our hosts BRGM who organised an excellent day out. 

Saladis Springs Outside the St Marguerite bottled mineral water factory Taking soil gas flux measurements at St Marguerite

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