*4.2. Basic Characteristics of Groundwater Chemistry*

The groundwater facies types in the study area were determined by calculating first the relative content of anion and cation in the collected groundwater, and then drawn the Piper diagram (Figure 3). Actually, the groundwater facies type can be determined by plotting groundwater sample points in all three zones (2 triangles and 1 diamond) of the Piper diagram [18].

Through the comparison between the calculation and Piper diagram [19], it was found that among the 14 groundwater sample points, 2, 2, 3, and 7 sampling points fall in HCO<sup>3</sup> <sup>−</sup>−Mg·Ca, HCO<sup>3</sup> <sup>−</sup>−Na, HCO<sup>3</sup> <sup>−</sup>−Na·Ca, and HCO<sup>3</sup> <sup>−</sup>−Na·Mg type zones, respectively, which suggests complex hydrochemical characteristics of groundwater in the study area [20–22]. The spatial distribution of groundwater facies types in the study area is shown in Figure 4.

It can be seen from Figure 4 that the HCO<sup>3</sup> <sup>−</sup>-Na·Mg facies type of groundwater was observed in a major part of the study area, covering mainly the east-central part of Yongqing Township, Houyi Township, Liujie Township, and the eastern part of Longhuzhuang Township. Whereas HCO<sup>3</sup> <sup>−</sup>−Na, HCO<sup>3</sup> <sup>−</sup>−Mg·Ca, and HCO<sup>3</sup> <sup>−</sup>−Na·Ca facies types were mainly distributed in the southwestern part of the urban area of Yongqing Town, the western part of Yongqing town, and the western part of Longhuzhuang Township, respectively. In addition, the groundwater facies types in the study area are more complex, which suggests influences of human activities on the hydrochemical characteristics of groundwater in the shallow aquifer in the study area [23].

*Water* **2022**, *14*, x FOR PEER REVIEW 7 of 17

**Figure 3.**Piper diagram of phreatic groundwater in the study area. **Figure 3.** Piper diagram of phreatic groundwater in the study area. Figure 4.

**Figure 4. Figure 4.** Zoning map of groundwater facies types in the study area. Zoning map of groundwater facies types in the study area.

Overall, the relative contents of HCO<sup>3</sup> <sup>−</sup>, Ca2+, and Mg2+ were higher in fresh and brackish water with low TDS. Water facies types and ion abundances in groundwater were consistent with these hydrochemical results. Yongqing County is located in the alluvial fan plain in front of the Taihang Mountains. The general flow trend of the shallow groundwater is from northwest to southeast runoff. However, the local groundwater flow direction in some areas in Yongqing County is northeast-southwest due to the impact of

**Figure 4.** Zoning map of groundwater facies types in the study area.

the local groundwater landing funnel [24]. Groundwater facies types are mainly influenced by rainfall infiltration and lateral runoff, resulting in low TDS and mineralization of groundwater. The groundwater facies type was mainly represented by the bicarbonate facies type, which suggests the dissolution of calcite, dolomite, and other carbonate minerals from the Taihang Mountains.
