## 5 Conclusions  
In this study, the distribution pattern of hydrogeochemical characteristics at a contaminated site in Xinxiang was analyzed by combination of multivariate statistical analysis and hydrochemistry, and the following conclusions were drawn.  
1. The hydrochemical type of groundwater in the study area have obvious differences in the horizontal and the vertical directions, reflecting the influence of the chromium slag pile on groundwater. In the shallow groundwater, the groundwater below the chromium slag heap is the SO\({}_{4}\)-HCO\({}_{3}\)-Na type, the hydrogeochemical composition east of the chromium slag heap and in the midstream is the HCO\({}_{3}\)-Cl-Mg-Ca type, and the downstream is basically uncontaminated with the HCO\({}_{3}\)-Mg-Ca-Na type. The deep groundwater shows the HCO\({}_{3}\) type.
2. Gibbs plots, ion ratios and saturation index indicated that the hydrogeochemical characteristics of the study area are mainly controlled by water-rock action and evaporative crystallization, with dissolution of halite, gypsum and anhydrite, precipitation of aragonite, calcite and dolomite, and precipitation of trivalent chromium minerals other than CrCl\({}_{3}\) and dissolution of hexavalent chromium minerals occurring in the groundwater of the site.
3. The groundwater in the study area is generally alkaline with a minimum pH of 7.55, which is conducive to the precipitation of trivalent chromium and the dissolution of hexavalent chromium. With the increase of pH, the saturation index of dolomite, calcite, aragonite and MgCr\({}_{2}\)O\({}_{4}\) keeps increasing, and these minerals are more likely to precipitate. The saturation index of Na\({}_{2}\)Cr\({}_{2}\)O\({}_{7}\), K\({}_{2}\)Cr\({}_{2}\)O\({}_{7}\) and CrCl\({}_{3}\) is decreasing, and the more easily Na\({}_{2}\)Cr\({}_{2}\)O\({}_{7}\), K\({}_{2}\)Cr\({}_{2}\)O\({}_{7}\) and CrCl\({}_{3}\) dissolve, and the saturation index of the remaining minerals is less affected by the change of pH.
4. Currently, the groundwater at the site is heavily contaminated and the groundwater chemistry type is altered. First, we should analyze the effects of other contaminants on chromium remediation in conjunction with indoor experiments. Second, we should maintain the concept of joint management of soil and groundwater. Third, the site groundwater runoff conditions are relatively poor and can be remediated by permeable reactive barriers technology and in situ injection of pharmaceuticals.  
Formal analysis, Y.C. and Q.Z.; investigation, Y.Z., Y.S., W.S. and Z.L.; writing-original draft preparation, W.C.; writing-review and editing, W.C. and Y.Z. (Co-first authors); supervision, Y.C. and Q.Z. All authors have read and agreed to the published version of the manuscript.  
This research is funded by Science and Technology Research Project of Henan Provincial Department of Natural Resources (Yu Natural Resources Letter [2019] No. 373-8); National Key R&DProgram of China (No. 2019 YFC1804801).  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
We sincerely thank the reviewers for useful comments and suggestions.  
The authors declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.