# A PHREEQC-Based Tool for Planning and Control of In Situ Chemical Oxidation Treatment
## 3 Results
### Testing the ISCO Modelling Tool
#### 3.2.3 Data Visualisation--Parts A3 and A4 of the Tool  
Another important function that can be used for planning or adjusting injections is the visualisation of real-time and periodic monitoring data, as well as modelling results. In this way, areas where injections should be placed, areas where injection is efficient, and, finally, areas where oxidation is recalcitrant can be identified. A monitoring of the baseline parameters showed a significant increase in the pH up to 11 in MW1A 5 days after injection. The front of the higher pH values (between 7 and 9) extended across the area from the borehole MW1 eastwards to MW2 approximately two weeks after injection (Figure 4), which could indicate the flow of the oxidising agent. The first sampling campaign after injection showed the highest temperature in MW1B with up to 16.2 \({}^{\circ}\)C. Two weeks after injection, the temperature remained high and fluctuated between 16 and over 18 \({}^{\circ}\)C, which could indicate the spread of the oxidising agent to the east (Figure 5). Measurements of toluene showed slightly elevated and dispersed concentrations of this pollutant immediately after injection and a decrease during the next sampling campaign over almost the entire area, which was direct evidence that the oxidiser was targeting this pollutant. High concentrations of this pollutant were only detected in the northern part of the area, which can be explained by a lateral flow of the pollutant from the source or by the effect of the rebound from the more impermeable soils (Figure 6). Figure 3: Example of an alarm plot for monitoring well MW1A where the pH had exceeded the acceptable level at the start of injection (17 March) and then stabilised within the expected range. Ethybenzene was the most problematic COEC in the study area, with measurements a few days after the injection showing very high concentrations in the south and relatively low concentrations in the rest of the study area (Figure 7). Two weeks after the event, the trend reversed while ethylbenzene concentrations remained low in the centre, which can be explained by the spread of the oxidant. In the northern part, the concentrations were  
Figure 4: Map showing the pH for (**a**) 5 days after the injection and (**b**) 20 days after the injection. Figure 5: Map showing the temperature (\({}^{\circ}\)C) for (**a**) 5 days after the injection and (**b**) 20 days after the injection. Figure 6: Map showing toluene concentrations (\(\upmu\)g/L) for (**a**) 5 days after the injection and (**b**) 20 days after the injection. still very high, which was probably due to the rebound of the pollutants as, during the last sampling campaign (not shown), the amount of ethylbenzene increased both near the southern and the northern border. Maps for the modelled values of the various parameters can also be displayed. In general, the geochemical model showed a quite good accuracy with respect to the spatial phenomena related to the injection of the oxidising agent. With regard to toluene, for example, the model showed both the consumption of the oxidising agent and the decreasing concentration of this pollutant in the central part of the study area and the rebound in the vicinity of well MW3 to the values observed during the sampling campaigns. The model also showed stable and low concentrations of ethylbenzene near the injection well and a recovery in the more distant wells, but the modelled recovery wave was delayed by about 10 days compared to the last sampling campaign (Figure 8). To summarise, the maps of the COECs and other parameters based on observed data can be very helpful for delineating zones where the oxidation is progressing from areas to where the process is not progressing satisfactorily due to unexpected circumstances such as rebound or strong heterogeneity.