ASSESSMENT REPORT

Hydrogeological Assessment Before Drilling – Plot 0212, 44230 Saint-Sébastien-sur-Loire, France

The report will be delivered as a PDF file

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

9. PRELIMINARY BOREHOLE LOCATION

• Zone A (Preferred): Central/northern open area of plot 0212, allowing easier access while remaining away from property boundaries and potential sources of anthropogenic contamination.

• Zone C (Unfavorable): Heavily wooded areas or locations immediately adjacent to ditches/surface runoff due to contamination risks and difficult access for equipment.

• GPS coordinates of the borehole target : LATITUDE 47.193245°N LONGITUDE -1.475893°W

10. INITIAL BOREHOLE DESIGN

• Exploratory depth: 50 m.

• Maximum reasonable depth: 60 m.

• Indicative diameter: 165 mm (down-the-hole hammer).

• Casing: Temporary casing in the upper section (through the clay formations) and permanent food-grade PVC casing in the main section.

• Screened intervals: Strictly defined according to the actual geology (opposite groundwater inflows and fractured intervals).

• Development: Jetting or piston pumping to remove fines and stabilize the filter pack.

11. ADAPTIVE STRATEGY (IF / THEN RULES)

• IF a thick and persistent clay layer is encountered beyond the preliminary forecast:

  THEN extend the temporary casing to ensure borehole-wall stability before entering the bedrock.

• IF a significant and early groundwater inflow appears within the first metres of the bedrock:

  THEN assess its stability and determine whether the target yield has been reached before reaching the maximum depth.

• IF the bedrock proves to be compact, fresh and completely devoid of fractures at 50 m:

  THEN reassess whether continuing to 60 m is appropriate or stop the drilling operation to avoid unnecessary costs.

12. RISK ANALYSIS

13. WATER QUALITY

• The presence of water does not mean that the water is potable.

• Risks of mineralization, iron/manganese, or diffuse pollution (nitrates from agricultural or urban sources) cannot be ruled out in this peri-urban area.

• Before any human consumption: Appropriate physicochemical and microbiological analyses must be carried out by an accredited laboratory.

14. ANALYSIS SUMMARY

15. FINAL SUMMARY

1. Does the borehole appear relevant? Yes, subject to conditions.

2. Why? Consistency with the regional hydrogeological context and surrounding boreholes, subject to confirming the actual fracturing of the bedrock.

3. Where is the primary target? Within the altered and fractured schistose/granitic bedrock, between 25 m and 45 m depth.

4. What is the secondary target? The weathered material–fresh bedrock interface or deeper fracturing down to 55 m.

5. What is the productivity potential? An indicative range of 1.0 m³/h to 2.5 m³/h, to be confirmed by a pumping test.

6. How deep should the exploration go? An exploratory depth of 50 m, extendable to 60 m if encouraging fracturing is encountered.

7. Where should the borehole be located? In the accessible and open central area of plot 0212.

8. What is the initial design? Down-the-hole hammer, protective casing through the first 10–15 metres of clay-rich formations, and installation of screens adapted to the groundwater inflows identified.

9. How should the design evolve? Strict adjustment of screen depths and the final stopping depth according to the actual groundwater inflows encountered during drilling.

10. What are the main uncertainties? The local intensity of bedrock fracturing and the exact thickness of the superficial clay-rich formations beneath the specific plot.

16. ASSESSMENT LIMITATIONS

This study constitutes a preliminary geological and hydrogeological assessment carried out remotely based on the data available at the time of its preparation. It does not constitute a direct investigation of the subsurface. The geological formations, depths, groundwater levels, fractures, groundwater circulation patterns and productivity potentials presented may differ from the conditions actually encountered on site. Data from nearby boreholes are used as references and do not constitute direct observations of the study plot. Correlations between boreholes are interpretations and do not guarantee the exact continuity of geological formations at the local scale. A preliminary potential aquifer target does not automatically constitute a screened interval. The geology actually encountered during drilling must take precedence over any preliminary remote assessment. The borehole design is therefore preliminary and adaptive. Diameter, depth, casing, screens, filter pack, cementing and development must be adapted to the formations actually encountered and to the technical conditions of the drilling operation. No exploitable yield should be guaranteed in advance. Sustainable productivity must be confirmed by an appropriate pumping test. The physicochemical and microbiological quality of the water cannot be reliably determined remotely and requires appropriate testing. Applicable regulatory requirements must be verified with the relevant authorities and competent organizations before construction of the borehole.

APPENDICES — MAPS AND VISUAL ASSETS

Potential Aquifer Targets and Proposed Borehole Location

Appendix 2

7. DISTINGUISHING GROUNDWATER PRESENCE FROM PRODUCTIVITY

• Probability of groundwater presence: Medium to High.

• Productivity potential: Medium (estimated by sector-based analogy between 1 m³/h and 3 m³/h).

• Confidence: Medium (based on consistent indirect data but without direct investigation of the plot).

8. YIELD ESTIMATE

• No reliable yield can be estimated remotely. By analogy with the surrounding boreholes (showing yields of 1.3 to 3 m³/h), an indicative range of 1.0 m³/h to 2.5 m³/h may be considered, subject to encountering a productive fracture network.

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.

Appendix 1

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.

View an example of a hydrogeological assessment report prepared by MAZE GEOANALYSIS before borehole drilling. This remote assessment examines the geological and hydrogeological context of the site, identifies potential aquifer targets and proposes a preliminary borehole location.