## 3 Results  
### Tracers  
The tracers were analyzed using spectrofluorimetry in the CETRAHE lab at the University of Orleans (Table 5). The assay of each of these tracers was performed using a calibration curve established with the same tracer used for the test. It should be noted that the spectral analysis technique, via the characteristic excitation and emission spectra, makes it possible to confirm the presence of these fluorescent tracers even when the concentration is low and close to the detection limit, to avoid any confusion with the natural fluorescence of water. The maximum net concentrations obtained at each piezometer are summarised in Table 6.  
It thus appears that the PZ1 piezometer (upstream of the injection well) was not reached by the tracer plume and that the PZ2 BIS piezometer (5 m downstream) is the only piezometer where the presence of all the tracers was proven. Starting from PZ3, located 10 m downstream of the injection well, some tracers such as the Amino G Acid and the bromide were not detected. Starting from PZ5, located 30 m downstream of the injection well, sulforhodamine B was also no longer detected. At PZ6, the piezometer that is most removed (60 m downstream of the injection well), no tracer was detected in significant concentrations by the end of the monitoring period. Uranine and lithium are the only tracers that were detected in all the piezometers located downstream of the injection point, except at PZ6. These are thus the best-suited tracers for this hydrogeological context, the first one because it is easily detectable in situ (using a field fluorimeter) including at low concentrations (0.1 \(\mu\)g\(\cdot\)L\({}^{-1}\)) and the second one because it proved to be more conservative. For uranine and lithium, the results were also interpreted using TRAC software [18] considering [PERSON]'s analytical solution [19] for the brief injection of a mass of tracer into an infinite volume in flow (Equation (1)):  
\[C_{(x,y,t)}\ =\ \frac{m}{4\ b\ \pi\ \omega\ t\ \sqrt{D_{L}\ D_{T}}}\cdot\exp \left[-\frac{\left(x-u\ t\right)^{2}}{4\ D_{L}\ t}-\frac{y^{2}}{4\ D_{T}\ t}\right] \tag{1}\]  
where \(C_{(x,y,t)}\) is the concentration of tracer (kg\(\cdot\)m\({}^{-3}\)) at the point with coordinates (\(x\), \(y\)) (m) and at time \(t\) (s), \(m\) is the mass of injected tracer (kg), \(b\) the thickness of the aquifer (m), \(\omega\) the cinematic porosity (\(-\)), \(D_{L}\) the longitudinal dispersion (m\({}^{2}\cdot\)s\({}^{-1}\)), \(D_{T}\) the transversal dispersion (m\({}^{2}\cdot\)s\({}^{-1}\)), and \(u\) the real flow speed (m\(\cdot\)s\({}^{-1}\)). In the context of this test, the fixed parameters are \(m=10^{-3}\) kg, \(b=14\) m and \(x\) which corresponds to the distance of each piezometer from the injection well. Note that the y coordinate has been left free, which makes it possible to check whether the piezometers are properly aligned in the main flow axis of the aquifer with respect to the injection well. At PZ2 BIS, 5 m downstream of the injection well, the concentration peak was achieved on the day of injection itself at 11:44 for lithium and at 15:28 for uranine, that is, 1.15 and 4.83 h respectively after the start of injection (Figure 10). Despite this difference in transit time, the hydrodynamic parameters used for the calibration of the breakthrough curves are the same for the two tracers: only the retardation factor varies, being fixed at 1.0 for lithium and 1.6 for uranine. The cinematic porosity is thus equal to 1.40 \(\times\) 10\({}^{-2}\) and the permeability 1.10 \(\times\) 10\({}^{-3}\) m\(\cdot\)s\({}^{-1}\), values in accordance with those previously obtained in test pumping.