137 7. Hydrogeological flow logging and dye tracer tests on the Hydrogeological Experimental Site Borehole M05 (Fig. 3) is cased with PVC slotted screens oriented horizontally. The temperature log indicates that groundwater is cooler at 120 m depth (12.70 °C) than at 30 m depth near the surface (12.87 °C). Consequently, the geothermal gradient cannot account for this observation, and the presence of a cooler inflow around 120 m depth is confirmed by the flow log between 110 and 120 m. The velocity derivative shows that no additional flow disturbs the measurement down to 72–76 m, where the signal is perturbed on the derivative (variation in well radius?). Between 32-34 m a typical inflow is detected on the derivative curve. Borehole MP6B is uncased, and therefore the measurement is not affected by the presence of a screen (Fig. 4). On the temperature log, a pronounced inflection at a depth of 84 m indicates an inflow of water, which is confirmed by the flow log, showing two signal variations clearly highlighted by the derivative at depths of 77 m and 83 m. At the bottom of the borehole, the signal becomes more complex, with a decrease in flow velocity associated with vacuoles clearly visible on the OPTV borehole wall imaging. A variation in the diameter of the open hole may account for the velocity decrease observed between 92 and 100 m. Figure 3 M05 Flowmeters log with pumping in M05. Figure 4 MP6 Flowmeters log with pumping in MP6.
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