*3.4. Evaluation of Groundwater Quality*

According to the Groundwater Quality Standard (GB/T 14848-2017), the comprehensive overstandard rate of groundwater in the study area was 60.53% by following the

inferior principle, and the overstandard indices were TH, F, NO3(N), TDS, CODMn, SO<sup>4</sup> <sup>2</sup>−, Na<sup>+</sup> , Cl−, NO2(N) and As. The statistical data of the overstandard indices are shown in Table 6 and Figure 9.


**Table 6.** Statistics of the overstandard indices.

*Rover*: Overstandard ratio based on the level III standard, %; *M*: Multiple of the maximum concentration to a multiple of the level III standard; Level III: Level III of Standard for Groundwater Quality (GB/T 14848-2017), mg/L. *Water* **2022**, *14*, 3168 19 of 26

**Figure 9.** Evaluated results of groundwater, the division of the I~V levels was based on the Standard for Groundwater Quality (GB/T 14848-2017) [28]. **Figure 9.** Evaluated results of groundwater, the division of the I~V levels was based on the Standard for Groundwater Quality (GB/T 14848-2017) [28].

The indices (TH, TDS, F–, Na+ and Cl–) in groundwater exceeded the standard, mainly due to natural factors. The climate in the study area is arid, evaporation is intensive, the groundwater flows slowly due to the gentle terrain, and the background contents of F– in some areas are high. All these factors led to the overstandard of these indices. The concentrations of NO3(N) and NO2(N) in some areas exceeded the standard. According to Table 6, the highest concentration of NO3(N) was 4.74 times that of Level III, and the concentration of NO2(N) was 1.35 times that of Level III. Combining Table 3 and Figure 3, the spatial variations in NO3(N) and NO2(N) in the study area were strong, indicating that the contents of NO3(N) and NO2(N) were influenced by human activities. CODMn is a common index to reflect the pollution of organic oxidizable substances in groundwater [66]. CODMn in the study area had a strong spatial variability. Concentrations of CODMn in some zones were higher than 3 mg/L, indicating that the synthetic organic compounds caused the deterioration of the groundwater environment by human factors. The indices (TH, TDS, F−, Na<sup>+</sup> and Cl−) in groundwater exceeded the standard, mainly due to natural factors. The climate in the study area is arid, evaporation is intensive, the groundwater flows slowly due to the gentle terrain, and the background contents of F − in some areas are high. All these factors led to the overstandard of these indices. The concentrations of NO3(N) and NO2(N) in some areas exceeded the standard. According to Table 6, the highest concentration of NO3(N) was 4.74 times that of Level III, and the concentration of NO2(N) was 1.35 times that of Level III. Combining Table 3 and Figure 3, the spatial variations in NO3(N) and NO2(N) in the study area were strong, indicating that the contents of NO3(N) and NO2(N) were influenced by human activities. CODMn is a common index to reflect the pollution of organic oxidizable substances in groundwater [66]. CODMn in the study area had a strong spatial variability. Concentrations of CODMn in some zones were higher than 3 mg/L, indicating that the synthetic organic compounds caused the deterioration of the groundwater environment by human factors.
