## 4 Results and Discussion
### Spatial Distribution Characteristics of Groundwater Chemistry
#### 4.2.2 Spatial Distribution Pattern of Ions  
Based on the analytical results of shallow groundwater samples, the spatial distribution pattern of ions was analyzed to study the spatial contamination characteristics of each ion component in groundwater (Figure 4a). The pollutant correlation coefficient matrix was plotted using R (Figure 4b). The Pearson's correlation coefficient was used to characterize the correlation between different pollutants. The TDS of 67% of the shallow groundwater samples exceeded three types of groundwater standards, especially the TDS concentration below the chromium slag pile and near the slag pile was the highest, and the water quality was poor, which was seriously affected by the chromium slag pile. Among the tested samples, the total hardness of 97% of the groundwater samples exceeded three types of groundwater standards, and the distribution of total hardness was similar to that of Ca\({}^{2+}\) and Mg\({}^{2+}\) concentration distribution, and the correlation coefficient reached 75%, indicating that the total hardness was mainly affected by the Ca\({}^{2+}\) and Mg\({}^{2+}\). The SO\({}_{4}\)\({}^{2-}\) concentration of 51% of the groundwater samples exceeded three types of groundwater standards, and the distribution of sulfate concentration was extremely similar to that of TDS, and the correlation coefficient reached 95%. Generally, SO\({}_{4}\)\({}^{2-}\) ions came from the dissolution of gypsum or sulfate sedimentary rocks. However, it can be seen that a large amount of sulfuric acid was used in the production of chromium salt, so it can be concluded that the SO\({}_{4}\)\({}^{2-}\) exceeded the standard in groundwater and was closely related to the production of chromium salt, and the correlation coefficient with Cr(VI) reached 83%. The NO\({}_{3}\)\({}^{-}\) concentration of 92% of the groundwater samples exceeded three types of groundwater standard. Na\({}^{+}\) concentration distribution was similar to that of TDS and SO\({}_{4}\)\({}^{2-}\) with a correlation coefficient of 96%, and the correlation coefficient between Na\({}^{+}\) and Cr(VI) was 0.72, mainly due to the fact that a large amount of sodium chromate and sodium sulfate will be produced in the chromium salt production process, resulting in the exceedance of Na\({}^{+}\) concentration in groundwater. The exceedance of Fe and Mn reached 74% and 70%, respectively. The exceedance of Cr(VI) was 49%, which had a certain contribution rate to TDS, and the correlation coefficient reached 78%. Pb and Hg  
Figure 4: (**a**) Exceedance rate of each component of groundwater, (**b**) pollutant correlation coefficient matrix. concentrations in groundwater samples had low exceedance rates, which may be related to human activities. Spatial Distribution Pattern of Ions in Deep Groundwater  
According to the analysis results of deep groundwater samples, it can be concluded that the total hardness of 68% of the tested samples exceeded the three groundwater standards, and the distribution of total hardness was similar to the distribution of Ca\({}^{2+}\) and Mg\({}^{2+}\) concentrations, with a correlation coefficient of 75% (Figure 5). The over-standard rate of TDS was 16%. For cations, Mg\({}^{2+}\) had the highest correlation coefficient with TDS, reaching 0.81, followed by Cr(VI), reaching 0.79, indicating that Mg\({}^{2+}\) contributed the most to the increase of TDS, and for anions, SO\({}_{4}\)\({}^{2-}\) had the highest correlation coefficient with TDS, reaching 0.89, indicating that SO\({}_{4}\)\({}^{2-}\) contributed the most to the increase of TDS. Na\({}^{+}\) exceeded the standard by 5%, and the correlation coefficient reached 79% with hexavalent chromium. The over-standard rate of NO\({}_{3}\)\({}^{-}\) was 79%. The over-standard rates of Fe and Mn reached 68% and 74%, respectively, which were comparable to those of Fe and Mn in shallow groundwater. The 58% of Cr(VI) concentration exceeded the standard in deep groundwater, and the highest correlation coefficient between Cr(VI) and SO\({}_{4}\)\({}^{2-}\) reached 0.92.