# Behaviour of PPCP Substances in a Fluvial Aquifer after Infiltration of Treated Wastewater
## 4 Results
### Evaluation of Groundwater Flow Velocities and Clogging  
All the hydraulic experiments conducted at Kojetin experimental site, including several pumping tests and VSK infiltration, were analysed using MODGLOW-USG software [22]. Inflow tests were carried out in the period 26 October 2021-16 December 2021 (length 52 days). The CP wells and the VSK well are 50 and 80 m from Morava, respectively. After the completion of the pumping of the CP1 and CP2 wells and at the end of the period, short recovery tests were carried out. The maximum withdrawal reached in the final phase of inflow tests, when pumping the VSK well, was 4 L/s. For well CP1, the value of hydraulic conductivity kf was determined in the range of 1.3 \(\times\) 10\({}^{-3}\)-1.8 \(\times\) 10\({}^{-3}\) m/s, for well CP2 in the range of 1.3 \(\times\) 10\({}^{-3}\)-1.8 \(\times\) 10\({}^{-3}\) m/s and for well VSK in the range of 9.1 \(\times\) 10\({}^{-4}\)-1.2 \(\times\) 10\({}^{-3}\) m/s. The model simulations described the period of inflow tests at wells CP1, CP2 and VSK. Model calibration consisted in optimizing the agreement between measured and simulated groundwater levels. The agreement of the model and measurements was achieved by a combination of manual and semi-automatic tuning of selected hydraulic parameters of the model. The model simulation faithfully affected the observed development of the levels, including the tested wells. The withdrawals were simulated using the Neuman boundary condition (the pumped amount of groundwater was entered) and the groundwater level in the pumped wells was calculated by the model (see example Figure 4). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**CONCENTRATION OF OXYPURINOL IN ng/L**} \\ \hline
**Date of Sampling** & **WWTP** &
\begin{tabular}{c} **MORAVA** \\ **RIVER** \\ \end{tabular} & **CP1** **WELL** & **PZ1** **WELL** & **PZ5** **WELL** \\ \hline
**7 November 2022** & 10200 & 729 & \textless{}50 & \textless{}50 & 270 \\ \hline
**20 November 2022** & 13400 & 2350 & \textless{}50 & \textless{}50 & 540 \\ \hline
**24 November 2022** & 17100 & 1960 & 338 & \textless{}50 & 438 \\ \hline
**30 November 2022** & 21800 & 2270 & 849 & 299 & 328 \\ \hline
**8 December 2022** & 14700 & 3050 & analysis error & 811 & 427 \\ \hline
**12 December 2022** & 12300 & 1600 & 1690 & 1070 & 366 \\ \hline
**AVERAGE** & 14917 & 1993 & 550 & 363 & 395 \\ \hline
**MEDIAN** & 14050 & 2115 & 379 & 150 & 400 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Time development of Oxypurinol content at monitored objects. Figure 4: Comparison of measured and modeled groundwater levels, pumped borehole CP1. blue line—measured data, red points and line—simulated data. The transport of non-sorbing, non-reacting PPCPs from VSK well was simulated too. Figure 5 demonstrate the example of simulation of Sucralose content. The best agreement between measurement and model result was achieved with the aquifer porosity of 15%, which is the expected value when considering a fluvial aquifer. In accordance with the measurement, the model also predicted that the locality of the PZ5 well remained unaffected by transport from the VSK well. Model calculated breakthrough time (3-5 days) is shorter than observed (8-12 days), even though the model longitudinal dispersivity was reduced to 1 m to minimise dispersion. This suggests that during the initial phase of the transport process, sucralose was degraded. The same process probably took place which caused the initial content of this substance to be zero. We repeated the same experiments and calculations for oxypurinol and benzotriazole with practically identical results. Clogging of the VSK borehole was manifested by a huge difference in groundwater level response during the pumping and infiltration period. Throughout the proceeding pumping test, the water level in the VSK well decreased by 1 m, when 4 L/s were abstracted.