# Assessing Nitrate Contamination Risks in Groundwater: A Machine Learning Approach
## 3 Results and Discussions
### Groundwater Contamination Risk Evaluation  
This study seeks to locate and prioritize the most vulnerable regions in an area that could be the reason for groundwater contamination, and offers a scientific basis for groundwater protection and land use planning. ArcGIS Environment was utilized to produce the groundwater contamination risk map after obtaining the vulnerability (DRASTIC model), contamination (nitrate concentration), and probability maps (ML techniques) of the study area. The map was further classified into five categories based on the occurrence, namely very low, low, moderate, high, and very high groundwater pollution risks, as shown in  
Figure 6: Groundwater contamination incidence probability map: (**a**) BRT (**b**) SVM (**c**) ensemble (**d**) MDA. Figure 7. The northwestern region of the study area and the upper-middle region is mostly exposed to low to very low groundwater contamination risk. The main reason for the lower exposure is that most of the land here is composed of shrubs, and human settlements in these regions are scarce and highly dispersed. However, a very high to moderate level of nitrate groundwater contamination risk exists for the southwest and lower-middle regions of the study area. The main reason for this is the existence of wild animal waste and urban waste in these regions, due to the existence of human settlements. Moreover, the percentages of areas under different groundwater contamination risk classes are also measured and are shown in Table 5. The very low, low, moderate, high, and very high groundwater contamination risk classes encompass areas of 902.5, 1087.5, 1615, 427.5, and 617.5 km\({}^{2}\), respectively. Thus, more than 50% of the area is exposed to moderate to very high groundwater contamination risk, as is evident from Table 5.  
The land use map does not demonstrate a considerable relationship with the nitrate contamination map. The groundwater vulnerability map and high nitrate contamination areas are also observed in the extreme northern part of the study area, where the population is not particularly dense, and is more scattered. The extreme northern area contains elevated snow-covered mountains, and has less vegetation cover. However, it has been found that \begin{table}
\begin{tabular}{c c c} \hline \hline
**Risk** & **Percentage** & **Area (km\({}^{2}\))** \\ \hline Very Low & 19\% & 902.5 \\ Low & 25\% & 1187.5 \\ Moderate & 34\% & 1615 \\ High & 9\% & 427.5 \\ Very High & 13\% & 617.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Area division by groundwater contamination risk for the study area. Figure 7: Groundwater contamination risk map for the study area. the nitrate contaminants in snow and glaciers are the main source of contamination in this area. The high nitrate risk area includes the region of unconsolidated rocks. The area has many snowy glaciers that store a high amount of nitrates [96]. Moreover, the DRASTIC model does not consider the land use type, which shows the northern part as highly vulnerable. Furthermore, the major deposits in the area are silt and clay. Silt, constituting almost 70% of the area, restricts the water seepage due to the high compression. This is why the DRASTIC model does not show the southeastern part as more vulnerable. However, all of the ML models show that the northern part is less exposed, since the population in the majority of the area is considerably dispersed. In contrast, the areas with less vegetation and high land use are exposed to a fair amount of nitrate contamination. Moreover, the study conducted by [PERSON] et al. [3] using the DRASTIC model and a modified version of the DRASTIC model (DRASTICA) for groundwater vulnerability assessment along the CPEC route also indicated that more than 50% of the area is exposed to very high to moderate groundwater contamination risk. The study also concluded that the areas with high vulnerability are those with high population density and anthropogenic activities, which shows that the outcomes are very much similar to the outcomes of the present study.