# Behaviour of PPCP Substances in a Fluvial Aquifer after Infiltration of Treated Wastewater
## 5 Conclusions  
* An experiment consisting of the gradual infiltration of 2366 m\({}^{3}\) of treated wastewater over a period of 36 days into a fluvial sand-gravel aquifer demonstrated a diverse influence on the quality of groundwater. Of the 113 monitored PPCP substances, 80 were detected at the experimental site, of which 69 were in the WWTP discharge.
* Groundwater contained a non-negligible range of PPCP substances even before the start of the experiment (PZ1 12 substances, CP1 11 substances and PZ5 17 substances), which represent \"background\" values. The source of these, mainly pharmaceuticals, is bank infiltration from the Morava River. River water contains a similar range of PPCP substances as WWTP discharge, although mostly in much lower concentrations.
* The influence of infiltration into the VSK infiltration well was manifested by changes in chemistry about 50 m away with a delay of 8-12 days.
* Of the monitored PPCP substances present in WWTP discharge, roughly half did not appear in the groundwater at all. It shows the selectively high degree of natural attenuation of the fluvial gravel sand sediments for some substances.
* On the other hand, a group of substances such Oxypurinol or Benzotriazole, which are often contained in treated wastewater in concentrations of the order of thousands of ng/L, migrated with groundwater, despite the fact that they were not detected as background values. Probably some degree of degradation of these occurred in the aquifer.
* Due to the lack of long-term medical studies that would document the possible negative impact of the detected substances on human health, the only option is to use the precautionary principle. Until a more efficient wastewater treatment technology is applied, it is clear that, despite the very good attenuation capacity of the rock environment for some substances, the infiltration of treated wastewater remains a problematic issue.
* However, this depends on the purpose for which the infiltration technology would be used. Both surface and shallow groundwater (in some places) in Central Europe already contain a non-negligible amount of PPCP substances. Therefore, in regions suffering from a lack of water for agricultural purposes, it would be possible potentially to infiltrate WWTP output into groundwater in accordance with current Czech legislation. After purification, these newly generated sources of groundwater could be used for irrigation in the event of a lack of another water source.  
[PERSON] and F.P. prepared the manuscript and approved the manuscript, including graphical and statistical interpretations. [PERSON] was responsible for the overall coordination of the research and editing of the manuscript. All authors have read and agreed to the published version of the manuscript.  
This research was completed with support from the project \"Water retention in the landscape using artificial recharge as a tool in the fight against drought\". This project has received funding from the Technology Agency of the Czech Republic, SS--Programme of applied research, experimental development and environmental innovation SS01020275.  
Data Availability Statement: Data is available through the T.G. Masaryk Water Research Institute, Prague.  
The authors declare no conflict of interest.