# A PHREEQC-Based Tool for Planning and Control of In Situ Chemical Oxidation Treatment
## 4 Discussion and Conclusions  
The problem of soil and groundwater pollution from the extraction, transport, use, and processing of hydrocarbons is expected to increase as demand grows. Consumption of petroleum hydrocarbons is expected to rise to 106.6 million barrels by the end of 2030 [90]. Today, there are millions of contaminated sites in Europe alone, only a tiny fraction of which have been remediated. According to some reports, almost 9 million tonnes of oil are discharged into aquatic environments worldwide every year [91]. Many organic pollutants pose a major environmental threat to natural ecosystems and human health, and the long-term sources of residual contamination occur due to their persistence, solidification, and tendency in becoming trapped [92; 93; 94]. Therefore, the identification of contaminant sources and the selection of the best removal/treatment method and control of the entire process is a global issue [95; 96]. The endeavour to remove contaminants and develop the most environmentally neutral methods of treating soil and groundwater is not only about current conditions and compliance with current standards,  
Figure 15: Relationship between the observed ethylbenzene concentrations and PHREEQC model predictions. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**COEC**} & **Initial Second-Order Rate** & **Second-Order Rate Constant after** \\  & **Constant [M\({}^{-1}\)s\({}^{-1}\)]** & **Calibration [M\({}^{-1}\)s\({}^{-1}\)]** \\ \hline Benzene & \(7\times 10^{-6}\) & Mean \(8.25\times 10^{-6}\) Median \(7.25\times 10^{-6}\) \\ Toluene & \(5.7\times 10^{-4}\) & Mean \(1.4^{-4}\) Median \(1\times 10^{-4}\) \\ Ethylbenzene & 0.007 & Mean \(1.2^{-4}\) Median \(7\times 10^{-5}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The initial and final values of the oxidation rates for the site in Flanders. but also about long-term sustainability goals [97; 98], which thus forces us to think about future needs and resource scarcity. Natural attenuation processes are being considered as a method of remediating sites contaminated with hydrocarbons. They have the advantage of being inexpensive and having little impact on the environment, but they tend to be slow, so they often need to be improved and their efficiency studied in order to achieve satisfactory levels of removal in a reasonable time [99; 100; 101]. On the other hand, the pump-and-treat method is costly, long-term, and complicated [102]. Therefore, there is still room for cost-effective and smart in situ technologies that are faster and can be adapted to different sites and COECs [103; 104]. In parallel with the development of treatment methods, increasingly sophisticated monitoring and risk assessment tools are being developed. The near real-time flow of information between devices, modelling tools, and operators could significantly improve the effectiveness of remediation. Key to this is not only communication between databases collecting information and modelling, but also trained experts and feedback from stakeholders [97]. The ISCO method is becoming increasingly popular, but this growing importance is not reflected in the modelling tools available to help experts in the field. To fill this gap, a tool based on the open-source software PHREEQC 2.18.0 and the Python language was developed. This article focuses on this user-friendly tool, which offers data storage and visualisation, simple remote control functions, and real-time and predictive responses to oxidant injection. Firstly, all practitioners know that good planning and minimising the risk of failure is the key to a successful ISCO. Even a short plan that includes all site-specific information, targets, and the required oxidiser dose can be very helpful in achieving good reagent delivery. To fulfil the expectations of practitioners, the aforementioned tool includes a brief calculation of critical ISCO parameters such as the radius of influence, the actual velocity of groundwater mixed with the oxidant, and the volume of contaminated soil.