## 4 Results and Discussion
### Results of Comprehensive Vulnerability Assessment and Its Validation
#### 4.2.2 Validation for the Mapping of Groundwater Vulnerability  
Groundwater with high vulnerability is more easily contaminated and thus more likely to have poorer water quality conditions. Currently, there are fewer methods to validate the vulnerability of groundwater, and the pollution distribution of \"NO\({}_{3}\)\", NO\({}_{2}\)\", NH\({}_{4}\)\" is generally used to compare with the vulnerability distribution of groundwater [47; 48]. [PERSON] et al. utilized single and combined factors to evaluate the water quality of groundwater, and then examined the correlation between the evaluation level and the vulnerability index [49]. [PERSON] et al. chose typical water quality indicators characterizing groundwater taste, color, and scaling, which were selected to calculate the value of the groundwater pollution index according to the \"Groundwater Quality Evaluation Standards\" [50], and then compared them with the spatial distribution of groundwater vulnerability. Since this study also addresses the vulnerability of shallow groundwater, and there are similarities with the above studies, similar validation methods were selected.  
We selected 11 water quality indicators (in Table 4) from nearly 30 well sites to calculate the Groundwater Pollution Index (GPI), which summed every index up after assigned number based on different categorization criteria in Table 4. The GPIs, ranging from 26 to 72, were used to validate the groundwater vulnerability and mapped in Figure 5, which demonstrates that high groundwater vulnerability corresponded to a high groundwater pollution index. These two were in high agreement, with a \(R^{2}\) coefficient of 0.961, as shown in Figure 6. This certificated that the GIS-based DRASTIC model for groundwater vulnerability assessment was scientific and reliable, and could provide reliable experience for groundwater pollution prevention and management.  
Figure 5: The mapping of groundwater vulnerability index and groundwater pollution index.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Assigned** & **pH** & **TH** & **TDS** & **F\({}^{-}\)** & **Cl\({}^{-}\)** & **SO\({}_{4}\)\({}^{2-}\)** & **NO\({}_{3}\)\({}^{-}\)** & **NO\({}_{2}\)\({}^{-}\)** & **Fe** & **Cu** & **Mn** \\
**Index** & **mg/L** & **mg/L** & **mg/L** & **mg/L** & **mg/L** & **mg/L** & **mg/L** & **mg/L** & **mg/L** & **mg/L** & **mg/L** \\ \hline
1 & 6.5–8 & 150 & 300 & 0.2 & 50 & 50 & 2 & 0.005 & 0.1 & 0.01 & 0.01 \\
3 & 6–6.5; 8–8.5 & 300 & 500 & 0.5 & 150 & 150 & 5 & 0.01 & 0.2 & 0.05 & 0.05 \\
5 & 5.5–6; 0.8; 5–9 & 450 & 1000 & 1 & 250 & 250 & 20 & 1 & 0.3 & 1 & 0.1 \\
7 & 1–5.5; 9–13 & 650 & 2000 & 2 & 350 & 350 & 30 & 4.8 & 2 & 1.5 & 1.5 \\
10 & 0–1; 13–14 & \textgreater{}650 & \textgreater{}2000 & \textgreater{}2 & \textgreater{}350 & \textgreater{}350 & \textgreater{}30 & \textgreater{}4.8 & \textgreater{}2 & \textgreater{}1.5 & \textgreater{}1.5 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Assignment criteria of groundwater pollution index.  
Figure 6: Groundwater vulnerability assessment and verification index correlation.