ASSESSMENT REPORT

Assessment of Plot 0212, Saint-Sébastien-sur-Loire, France

The report will be delivered in PDF format

High-precision Digital Terrain Model (LiDAR) of plot 0212, allowing the bare-ground topography to be visualized by removing vegetation.

1. IDENTIFICATION AND HIERARCHIZATION OF AVAILABLE DATA

• Level 1 — Direct Site Data (Plot 0212)

• Source: Cadastral extract and orthophotography of plot 0212 located at 6 bis rue du Vieux Puits, Saint-Sébastien-sur-Loire.

• Nature: Partly wooded area, bordered by developed plots and roads, moderate slope, with dense vegetation across the southern/eastern half.

• Distance from the site: 0 m (study site).

• Reliability: Very high (direct observation of the visual documents).

• Use: Determination of the site footprint, accessibility for drilling equipment and surface siting constraints.

• Level 2 — Direct Data from Reference Boreholes

• Borehole 1 (BSS: 04818X1094 / F): Located in Basse-Goulaine (220 rue des Coupries). Depth: 67.00 m. Geological sequence: alluvial deposits from 0 to 5.30 m, clay from 5.30 to 14.30 m, schistose bedrock from 14.30 to 67.00 m. Final yield: 3 m³/h. Equipped with casing and screens from 32 to 67 m.

• Borehole 2 (Ref. Lefeuvre / Tanguy): Located at 5 rue Georges Sand, Saint-Sébastien-sur-Loire. Depth: 52 m. Geological sequence: clay from 0 to 6 m, soft granite from 6 to 10 m, grey granite with quartz-bearing intervals from 10 to 52 m. Progressive water inflows with a final yield of 2.2 m³/h.

• Borehole 3 (Ref. 04818X0606 / Dousset): Located at 7 chemin de la Petite Galerne, Saint-Sébastien-sur-Loire. Depth: 49 m. Geological sequence: clay from 0 to 22 m, medium-hard schist with quartz-bearing intervals from 22 to 49 m. Final yield: 1.3 m³/h.

• Level 3 — Regional Data

• Geological context: Cenozoic/Quaternary superficial formations overlying a metamorphic Paleozoic basement (schists and granitic massifs of the Namnetian/Armorican region).

• Level 4 — MAZE Interpretation

• Probable presence of a superficial clayey-silty cover of variable thickness (approximately 5 to 20 m depending on topographic position), overlying a fractured schistose or granitic basement potentially constituting the main aquifer..

2. TOPOGRAPHIC AND GEOMORPHOLOGICAL ANALYSIS

• Topography : The plot has a general slope oriented towards the north/northeast, in the direction of the Loire.

• Geomorphology : Intermediate to lower slope position. Nearby low-lying areas may favor the potential accumulation of unconsolidated formations (weathered materials or older alluvial deposits).

• Equipment access : Access to plot 0212 requires consideration of the dense tree cover (southern part) and developed boundaries, requiring a targeted location for a mobile drilling rig.

3. PRELIMINARY GEOLOGICAL MODEL

4. HYDROGEOLOGICAL MODEL

• System type : Fractured-bedrock aquifer (unconfined to semi-unconfined depending on the thickness of the clay cover).

• Recharge / Circulation : Recharge occurs through effective infiltration in upstream outcrop areas and through weathered zones. Groundwater circulation is dependent on the fracture network and quartz veins intersecting the bedrock.

• Role of the formations : The upper clay-rich formations provide superficial protection to the groundwater system but constitute an obstacle to direct infiltration, while the fractured bedrock zones provide the productivity of the borehole.

5. ANALYSIS OF REFERENCE BOREHOLES

• Geological comparability : Good (presence of altered schistose/granitic bedrock typical of the area).

• Topographic comparability : Medium to good (geographically nearby area within the municipality of Saint-Sébastien-sur-Loire).

• Hydrogeological comparability : Good (water inflows associated with bedrock discontinuities).

• Usefulness for the site : High for calibrating the exploratory depth (between 45 m and 60 m) and anticipating the nature of the formations to be encountered. The nearby borehole provides an indication of the local potential, but its productivity cannot be directly transferred to the study plot.

6. IDENTIFICATION OF POTENTIAL AQUIFER TARGETS

• PRIMARY TARGET : Altered/fractured bedrock horizon between 25 m and 45 m, characterized by quartz-bearing intervals or shear zones favoring groundwater inflows.

• SECONDARY TARGET : Weathered material–fresh bedrock interface or deeper zones (up to 55 m) if fracturing persists.

• TARGET TO AVOID : The superficial clay cover (0–15 m), considered low-potential and prone to collapse, as well as fresh, unfractured bedrock beyond 60 m.