# A PHREEQC-Based Tool for Planning and Control of In Situ Chemical Oxidation Treatment
## 4 Discussion and Conclusions
Operators are also informed in real time about unexpected events and the arrival of the oxidising agent based on basic physical parameters. Since a picture is worth a thousand words, the advantage of this modelling tool is that the visualisation function, which also uses the Python language, facilitates the display of maps and XY plots of the observed and modelled data. This makes it possible to inform those responsible for remediation sites about what is really going on underground and to help them make further decisions. The main feature of the described tool is the hydrogeochemical model PHREEQC, which could be used to predict oxidant consumption within the expected impact radius and to predict pollutant degradation. The reactive transport model could be run prior to the injection as part of the design plan and during ongoing treatment, which is supported by calibration. The hydrogeochemical model allows for the prediction of changes in groundwater chemical status in two phases: injection until ROI is reached and a user-defined post-injection period during which the rebound of COECs could be predicted if the ion exchange in microporous water is added to the simulations. The latter could be crucial for long-term land use planning and the application of other remediation methods. It should be emphasised that the tool described is site-specific. It collects a variety of data specific to the area to be revitalised, such as background data on groundwater, contamination levels, and soil properties. In addition, soil structural heterogeneity is also taken into account by including hydraulic conductivity for each monitoring well, as well as by estimating groundwater velocity for each point where the oxidant release is observed and, more importantly, the actual velocity can be estimated based on the oxidant arrival for each observation point. COEC concentrations are also reported for each monitoring well. The following conclusions can be made:  
* The widely used PHREEQC code, Excel, and the Python programming language were combined to create a user-friendly and intuitive tool for researchers and practitioners in the field of in situ chemical oxidation;* The concept of the tool is feedback-orientated, i.e., it is intended to provide the expert on site with direct feedback;
* The use of real-time and regular monitoring and modelling provides scientists, practitioners, and managers with a good knowledge base and helps to improve the effectiveness of remedial measures;
* The proposed tool was successfully tested at the contaminated site to check all functions. The tool informs about the unexpected conditions (alarm), the arrival of the oxidant (visualisation), and the time needed to reduce COEC and to consume the oxidant (geochemical model);
* The developed tool helps to address two phenomena that are crucial for the remediation and fate of solutes: heterogeneity and the rebound of contaminants;
* The geochemical model was successfully calibrated, and the kinetic data were slightly modified during the process. The adjusted values could also be valuable for researchers as they fit the field conditions better than the values determined under controllable laboratory conditions;
* The development of tools that are free, based on open-source software, and are open to change is crucial for reducing costs and sharing experiences. The authors see opportunities for the presented tool to help ISCO practitioners improve the performance of this method. The presented tool can be further developed with regard to the use of other oxidising agents and tests at sites contaminated with other substances. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14093600/s1](https://www.mdpi.com/article/10.3390/app14093600/s1)]([https://www.mdpi.com/article/10.3390/app14093600/s1](https://www.mdpi.com/article/10.3390/app14093600/s1)), Table S1: Simple outcomes from the tool, a set of equations and reactions. Conceptualisation, K.S.-G. and R.U. ; methodology, K.S.-G. and R.U.