## 4 Results and Discussion  
In accordance with the hydrogeological and operational parameters discussed before, a numerical simulation was implemented to assess the thermal perturbation evolution during the yearly operation of the GSHP system and to verify the thermal interference in the Armi station wells. The outputs of the simulations are the hydraulic head distribution and the groundwater temperature distribution over time and space. The hydraulic heads distribution and the groundwater flow directions relative to Aquifer B are reported in Figure 6.  
The simulated piezometry was in accordance with the real one [40], with groundwater flow directed NW-SE. No important groundwater flow variations are expected during the duration of the heat transport simulations. The simulated groundwater temperature could not be validated due to the impossibility of performing temperature measurements in the MM wells invested by the thermal plume. The groundwater temperature was monitored for the whole simulation period at 2 different observation points (OBS 1 and OBS 2) located 5 and 80 m downgradient of the borefield, respectively. Such monitoring points are not physically present but were  
Figure 6: Simulated hydraulic head distribution in Aquifer B.  
introduced in the model just to analyze the groundwater temperature variation over the Aquifer Groups A and B (Figure 7). At the OBS 1 location (Figure 7a), the groundwater temperature in Aquifer A (Layer 1) decreases during the heating period (winter season), moving from the aquifer's unperturbed value (15.2 \({}^{\circ}\)C) to a minimum value of 10.8 \({}^{\circ}\)C. Instead, during the summer period, the temperature increases from 10.8 \({}^{\circ}\)C to a maximum value of 19.0 \({}^{\circ}\)C. Concerning Aquifer B (layer 5), the temperature decreases during the heating period (winter season), going from the aquifer unperturbed value (14.5 \({}^{\circ}\)C) to a minimum value of 11.1 \({}^{\circ}\)C; on the contrary, during the summer period the temperature increases from 11.1 \({}^{\circ}\)C to a maximum value of 17.8 \({}^{\circ}\)C. In Aquifer C (layer 9), the groundwater temperature has more inertial behavior due to the lower hydraulic conductivity of the aquifer material, ranging from 14.5 \({}^{\circ}\)C to 10.0 \({}^{\circ}\)C. At the OBS 2 location (Figure 7b), similar behavior of groundwater temperature was detected, but reduced groundwater temperature oscillations around the unperturbed value were observed. This is because OBS2 is located 80 m downgradient of the borefield, and therefore, the temperature is affected by the thermal gradient and advection phenomenon. At OBS 2, the groundwater temperature increases by a maximum of 3.5 \({}^{\circ}\)C and decreases by a maximum of 4 \({}^{\circ}\)C compared to the unperturbed value (Aquifer A), demonstrating that a thermal interference is still present. For the aforementioned reasons, if a new GSHP system were installed in this area, a problem related to the energy performance of the new system would be present. Specifically, the new GSHP system would work in a thermal-altered environment (not in an unperturbed condition), reducing the COP value during winter and the EER value during summer of about 10%, considering a COP reduction equal to 2.5% for 1 \({}^{\circ}\)C of groundwater temperature gain or loss, calculated from technical schemes of different heat pumps present in the market. To better evaluate the extent of the thermal perturbation downgradient of the borefield at fixed time (the latter heating period of the 3 rd year simulation), 90 monitoring wells were placed along the preferential groundwater flow direction (Figure 8). Figure 7: Groundwater temperature distribution inside (**a**) observation point 1 (OBS 1) and (**b**) observation point 2 (OBS 2). Figure 8 is a picture of the aquifer temperature downgradient of the BHE on the last simulated day.