Distribution of Groundwater Hydrochemistry and Quality Assessment in Hutuo River Drinking Water Source Area of Shijiazhuang (North China Plain)

Abstract

The Hutuo River Drinking Water Source Area is an important water source of Shijiazhuang (North China Plain). Knowing the characteristics of groundwater chemistry/quality is essential for the protection and management of water resources. However, there are few studies focused on the groundwater chemistry evolution over the drinking water area. In this study, total of 160 groundwater samples were collected in November 2021, and the spatial distribution of groundwater chemistry and related controlling factors were analyzed using hydrological and multivariate analysis. The entropy-weighted water quality index (EWQI) was introduced to assess the groundwater quality. The results show that the hydrogeochemical types of groundwater are Ca-HCO₃ (78.1%), mixed Ca-Mg-Cl (20%), and Ca-Cl (1.9%) in the area. Graphical and binary diagrams indicate that groundwater hydrochemistry is mainly controlled by water–rock interaction (i.e., rock weathering, mineral dissolution, and ion exchange). Five principal components separated from the principal component analysis represent the rock–water interaction and agricultural return, redox environment, geogenic sources, the utilization of agricultural fertilizer, the weathering of aluminum silicates, and dissolution of carbonates, respectively. More than 70% of the samples are not recommended for irrigation due to the presence of high salt content in groundwater. EWQI assessment demonstrates that the quality of the groundwater is good. The outcomes of this study are significant for understanding the geochemical status of the groundwater in the Hutuo River Drinking Water Source Area, and helping policymakers to protect and manage the groundwater.

1. Introduction

Groundwater is the most important water source for drinking, industrial, and agricultural water supplies in arid and semi-arid areas, which is essential for the sustainability of the ecosystem and human daily life [1]. Eighty percent of human diseases are induced by water, according to the World Health Organization [2]. Groundwater interacts with the surrounding environment during its process of formation and transportation, the physical and chemical interactions including dissolution/precipitation, adsorption/desorption, oxidation/reduction, and acid–base balance. The hydrochemical composition of groundwater and its distribution reflects the existence of the long-term interaction between groundwater and the environmental media [3]. Clarifying the distribution pattern of groundwater chemistry can help to understand the principal factors and processes that dominate the hydrochemical characteristics of groundwater. The results can provide a hydrochemical background for protecting the groundwater source of the North China Plain and other places.

The chemical evolution assessment is important for the establishment of suitable management policies and groundwater quality improvement. The hydrochemical composition characteristic of groundwater is controlled by sedimentary conditions and human activities [4]. However, it is difficult to figure out the contributions of geogenic processes and anthropogenic activities. Many analytical methods (multivariate statistical analysis, hydrogeochemical facies, binary diagrams, correlation analysis, etc.) are used to characterize the evolution processes [5,6,7]. Numerous indices have been developed to evaluate water pollution. Among them, the water quality index (WQI) is one of the most widely used indices to determine the overall groundwater quality [8]. The combination of entropy weights and the conventional WQI called the entropy water quality index (EWQI) is proposed; it can improve the reliability of the assessment results [9]. EWQI has been used by numerous studies for water quality assessment [10,11].

Shijiazhuang is one of the biggest cities located in the middle west part of the North China Plain, with a huge population [12]. Groundwater is the dominant source of drinking and irrigation water in Shijiazhuang [13]. However, the quantity and quality of groundwater are threatened with the development of urbanization and industrialization [14]. The demand for groundwater is increasing and the quality of groundwater is deteriorating due to the pollution emissions. The groundwater level has decreased sharply due to drought and over-exploitation, accompanied by the excessive nitrate loading and expansion of saline–alkaline land area [15,16,17]. Human activities lead to a dramatic increase in the groundwater NO₃⁻ concentration in pluvial fans of the Hutuo River, which reaches 124.4 mg/L [17]. The decreasing groundwater level will affect the redox environment, and may further affect the chemistry composition of groundwater. The dominant water types are Ca-HCO₃, HCO₃-Ca-Mg, and HCO₃-Na-K, as investigated 15 years ago. However, they have been transformed from HCO₃-type to HCO₃-Cl, HCO₃-SO₄, and SO₄-HCO₃ types in recent years [18]. Due to the variety of geological media and input from various anthropogenic sources, the distribution variability of groundwater chemistry and associated interactions remain unclear in this area.

The Hutuo River Drinking Water Source Area is located in the northern region of Shijiazhuang, and upstream of the water source are the Gangnan and Huangbizhuang reservoirs, which provide water for the Fourth and Seventh Water Plants of Shijiazhuang. The Hutuo River Drinking Water Source Area is an important water source in the North China Plain, and it is the water intake for the Shijiazhuang Drinking Water Company. However, there are few studies focused on groundwater chemistry evolution on the scale of drinking water areas. The hydrochemistry, origin analysis, and quality assessment of the groundwater in the Hutuo River Drinking Water Source Area have not been investigated comprehensively. Therefore, it is essential to analyze the geochemical characteristics in groundwater and the associated quality risks in water source areas. This study aims to: (1) measure the prevailing levels of 19 chemical variables based on national standards; (2) clarify the mutual associations among the measured parameters and the processes controlling the groundwater chemistry by statistical methods; (3) evaluate the suitability of the groundwater in the Hutuo River Drinking Water Source Area for irrigation/drinking. The study can provide a scientific support for the establishment or optimization of groundwater quality/quantity monitoring and management systems.

2. Materials and Methods

2.1. Site Description

Shijiazhuang (37°27′–38°47′ N, 113°30′–115°20′ E), is the capital of Hebei Province and located in the Mideast part of North China Plain, covering an area of 13,504 km². The average annual temperature of the study area is 13 °C. The annual precipitation of Shijiazhuang is 481.9 mm, and the rainfall is mainly concentrated in summer. The annual evaporation rate is 1557.8 mm/a, which is significantly higher than the mean annual precipitation. The Taihang Mountains are located in the western part of Shijiazhuang. The topography is low in the east and high in the west, with a slope of approximately 0.5~1.0‰. Quaternary deposits are distributed on the surface of the region, with sediments gradually thickening from west to east and particles becoming coarse to fine. The primary rivers are the Hutuo River and Ye River. According to the Adjustment Plan for Emergency Reserve Drinking Water Source Areas in the Main Urban Area of Shijiazhuang, the drinking water source areas of the Hutuo River are divided into first-level protected area (63.95 km²) and second-level protected area (196.84 km²) (Figure 1). According to the Technical Specification for Classification of Drinking Water Source Protection Areas of China (HJ 338-2018), sewage outlets and the cultivation and stocking of poultry and livestock are prohibited in the first-grade protection zone. The Hutuo River Drinking Water Source Area was established in 1971 with 77 water source wells, the designed water intake quantity is 9.49 × 10¹⁰ tons, and the actual water intake quantity is 8.79 × 10⁷ tons.

The survey area belongs to the top and middle sections of the Hutuo River alluvial fan in the Ziya River system. It is divided into the hydrogeological structure zoning of fissure karst and the hydrogeological structure zoning of loose rock pore aquifer within a depth of 120 m. Fissure karst water is distributed in the northwest of the survey area and is hidden fissure karst water. Loose rock pore water is distributed throughout the region, and the main water source for the Hutuo River system groundwater type water source is the second water bearing rock group of loose rock pore water.

2.2. Sample Collection and Analysis

In this study, 160 groundwater samples were collected in November 2021 from the Hutuo River Drinking Water Source Area. The location of sampling sites was recorded by real-time kinematic devices. For all the samples, well water was pumped several times before water sampling to ensure that freshwater samples were collected. Samples were collected from private wells with sampling depths below 0.5 m from the water table. The shallow groundwater table is buried at a depth of 10–35 m. Polyethylene bottles were cleaned three times by the groundwater before being collected. A quantity of 250 mL of groundwater was collected for analysis of iron (Fe²⁺), manganese (Mn²⁺), zinc (Zn²⁺), and aluminum (Al³⁺), and 1500 mL for analyses of pH, total hardness (TH), total dissolved solids (TDS), sodium (Na⁺), arsenic (As³⁺), chloride (Cl⁻), fluorine (F⁻), sulfate (SO₄²⁺), nitrate (NO₃⁻), nitrite (NO₂⁻), calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺). All the bottles were filled with groundwater and sealed with parafilm to avoid interference from atmospheric gases. In addition, to ensure the analysis reliability, HNO₃ (65%) was added to adjust the pH below 2 in the bottle. Afterward, groundwater samples were stored at 4 °C before laboratory analysis. All samples were analyzed at the Hebei Provincial Geological Experimental Testing Center, Baoding.

Seventeen chemical parameters were measured. The pH was measured using a portable acidity meter (Zhengzhou Baojing Electronic Technology Co., Ltd., Zhengzhou, China, PHS-3C). The total hardness was calculated using the gravimetric titration method. The total dissolved solids was estimated by a weighing method. Heavy metal ions (Zn²⁺, Al³⁺, Mn²⁺) were identified using Agilent Inductively Coupled Plasma Mass Spectrometry (ICP-MS, 7700XI); the detection limits of Zn²⁺, Al³⁺, Mn²⁺ were 0.67, 1.15, 0.12 µg/L, respectively. A detection limit of 0.3 µg/L was determined by an Atomic Fluorescence Photometer (Beijing Haiguang Instrument Co., Ltd., Beijing, China, AFS-8510). Major cations were detected by the Agilent Inductively Coupled Plasma Spectrometer (Agilent-725). The detection limits were 120 µg/L for Na⁺, 20 µg/L for Ca²⁺, 3 µg/L for Mg²⁺, 50 µg/L for K⁺, 10 µg/L for Fe²⁺. Quantification of anions (F⁻, SO₄²⁻, Cl⁻, NO₃⁻) was carried out by ion chromatography (Dionex, Sunnyvale, CA, USA, ICS-1100), and the detection limits were 6 µg/L for F⁻, 18 µg/L for SO₄²⁻, 7 µg/L for Cl⁻, 4 µg/L for NO₃⁻. NO₂⁻ was detected with a spectrophotometer (T6), and the detection limit was 3 µg/L. HCO₃⁻ and CO₃²⁻ were determined by a titration method (Method for Analysis of Groundwater Quality, DZ/T0064.49-2021) using an acid burette. Each sample was analyzed in triplicate, and standards and blanks were interspersed regularly in sample batches to ensure the data quality. All data were corrected for instrument drift. The relative errors of these parameters were < ±10%. In addition, the charge balance error percentage (%CBE) was checked. The %CBE of all water samples was < ±5%.

2.3. Statistical Analysis

The principal components (PCs) were calculated by the multivariate principal component analysis (PCA), and PCs were used to characterize the study object by dimensional reduction. In the PCA, PCs with eigenvalues greater than 1 are significant and can be used to describe the impact of hydrochemical processes and human activities on groundwater chemical components. The PCA and Pearson correlation were conducted through IBM SPSS Statistics 24. The Pearson correlation is calculated by:

$$r=\frac{{\sum }_{i=1}^n(X_i-X)(Y_i-Y)}{\sqrt{{\sum }_{i=1}^n{(X_i-X)}^2}\sqrt{{\sum }_{i=1}^n{(Y_i-Y)}^2}}.$$

2.4. Groundwater Quality Assessment

Sodium hazard can be described by the sodium adsorption ratio (SAR). It is an important index and can be calculated by the relative concentrations of Ca²⁺, Na⁺, and Mg²⁺ in the irrigation groundwater. The formula can be expressed as follows:

$$SAR=\frac{\left[{Na}^{+}\right]}{\sqrt{\frac{1}{2}(\left[{Ca}^{2+}\right]+[{Mg}^{2+}\left]\right)}}$$

Based on the United States Department of Agriculture (USDA), groundwater with a SAR less than 10 (more than 26) is considered ideal (inappropriate) for irrigation. Groundwater with a high SAR value and low/moderate salinity will decrease the aeration and infiltration rate of the soil, affect the normal condition of plant growth, and lead to crop yield reduction [19].

Residual sodium carbonate (RSC) can be calculated by the relative content of Ca²⁺, Mg²⁺, CO₃²⁻_, and HCO₃⁻ in the groundwater. The formula can be expressed as follows:

$$RSC=\left({{CO}_3}^{2-}+{{HCO}_3}^{-}\right)-({Ca}^{2+}+{Mg}^{2+})$$

Groundwater with an RSC value of less than 2.5 meq/L has been considered satisfactory for plant irrigation. Groundwater with a high RSC value would lead to rapid salinization and codification of the soil profile, thereby harming the growth of crops [20].

Salinity hazard can be described by potential salinity, which reflects the relative content of Cl⁻ and SO₄²⁻ in the groundwater.

$$PS={Cl}^{-}+\sqrt{{{SO}_4}^{2-}}$$

where ion concentrations are in meq/L. Groundwater with PS values more than 3 and 15 are considered conditioned and not recommended, respectively, which may cause accumulation of salinity in soil [21].

The entropy weight quality index (EWQI) method was applied to determine the quality of the groundwater. EWQI calculation (Figure S1) has been used by numerous studies due to its simple calculation process and the integration of multiple chemical parameters [22,23,24]. In this study, the groundwater quality indices including pH, TH, TDS, Fe²⁺, Na⁺, Al³⁺, Mn²⁺, Zn²⁺, As³⁺, F⁻, SO₄²⁻, Cl⁻, NO₃⁻, and NO₂⁻ were selected to identify the groundwater quality of Hutuo River Drinking Water Source Area. The EWQI can be calculated through two processes (Figure S1) [25]. The first step is the calculation of the rating scale ($q_j)$ of EWQI for the chemical parameters of groundwater. $C_i$ is the concentration of groundwater quality, $S_i$ represents the values of grade III standards in the groundwater quality standard limits of the People’s Republic of China. The $q_j$ of pH values was evaluated based on the standard pH of 6.5–8.5. The second step is the standardization of matrix; $C_{min}$ and $C_{max}$ are the minimum and maximum of the chemical parameters, respectively.

Groundwater can be classified into 5 levels according to EWQI value [26,27], including Level 1: excellent (25 > EWQI), Level 2: good (50 > EWQI > 25), Level 3: fair (100 > EWQI > 50), Level 4: poor (150 > EWQI > 100), Level 5: very poor (EWQI > 150).

3. Results and Discussion

3.1. Groundwater Hydrochemistry

The statistical analysis results of the groundwater chemical parameters in the Hutuo River Drinking Water Source Area are illustrated in

Table 1. Statics of chemical parameters of groundwater (unit: mg/L, except pH).

Parameters	Max	Min	Mean	SD	CV	Low Quartile	Upper Quartile	Allowable Limits a	Percentage Exceeding the Standard
pH	8.20	6.92	7.49	0.17	0.02	7.39	7.59	6.5–8.5	0.00
TH	1668.00	204.00	551.48	200.72	0.36	427.00	629.00	450.00	71.25
TDS	2371.00	271.00	747.29	284.70	0.38	574.00	872.00	1000.00	13.75
Fe2+	0.33	0.00	0.01	0.03	6.57	0.00	0.00	0.30	0.63
Na+	154.00	8.87	39.50	19.65	0.50	28.40	45.20	200.00	0.00
Al3+	0.05	0.00	0.01	0.01	1.09	0.00	0.01	0.20	0.00
Mn2+	0.07	0.00	0.00	0.01	2.56	0.01	0.00	0.10	0.00
Zn2+	2.44	0.00	0.05	0.21	3.80	0.04	0.03	1.00	0.63
As3+	0.00	0.00	0.00	0.00	1.38	0.00	0.00	0.01	0.00
F−	0.62	0.05	0.26	0.10	0.37	0.20	0.32	1.00	0.00
SO42−	552.00	11.00	191.84	93.03	0.48	141.00	238.00	250.00	20.00
Cl−	404.00	8.98	72.54	50.75	0.70	43.90	82.90	250.00	2.50
NO3−-N	104.00	1.79	17.23	13.27	0.77	7.65	22.40	20.00	30.63
NO2−-N	1.55	0.00	0.01	0.12	8.58	0.00	0.01	1.00	0.63
Ca2+	528.00	64.60	161.41	62.26	0.39	122.00	183.00	-	0.00
Mg2+	97.00	9.68	36.59	14.32	0.39	28.60	42.30	-	0.00
K+	23.60	0.36	2.15	2.19	1.02	0.97	2.60	-	0.00
CO32−	6.00	0.00	0.04	0.47	0.08	0.00	0.00	-	0.00
HCO3−	578.00	186.00	315.86	68.88	4.59	258.00	360.00	-	0.00

Note: ^a Allowable limits represent the values of grade III standards in the groundwater quality standard limits of the People’s Republic of China.

. The pH values range from 6.92 to 8.20 in groundwater samples. Only one groundwater sample has an acidic pH of 6.92, and all the other groundwater samples are slightly alkaline to neutral. The total hardness (TH) range is 204–1668 mg/L, with a mean concentration of 554.48 mg/L. The results reveal that 71.25% of the groundwater samples exceeded the allowable limit of TH (450 mg/L). TH is mainly originated from the dissolution of minerals and illustrates the total content of Mg²⁺ and Ca²⁺ [28]. Total dissolved solids (TDS) values of groundwater range from 271 to 2371 mg/L. The wide variation in TDS content indicates that various factors are correlated with the chemical composition of groundwater. The TDS values of the samples above 1000 mg/L are 13.75%, indicating that these groundwater samples are unsuitable for domestic consumption, leading to inferior palatability and gastrointestinal irritation. According to salinity classification [29], the groundwater in the Hutuo River Drinking Water Source Area is categorized into no-saline/fresh and low-saline water.

In the Hutuo River Drinking Water Source Area, the cationic dominance in the groundwater can be described in the following order: Ca²⁺ > Na⁺ > Mg²⁺ > K⁺. Ca²⁺ is the dominant cation over the area, ranging from 64.6 to 528 mg/L, with an average concentration of 161.4 mg/L (Table 1). Ca²⁺ may originate from the dissolution of Ca-rich minerals such as CaCO₃ and CaMg(CO₃)₂ during recharge. The second dominant cation is Na⁺; its concentration in the study area ranges from 8.87 to 154 mg/L. Na⁺ plays a crucial role as a salinity indicator in groundwater; it originates from various processes including ion exchange in halite and clay minerals, and plagioclase feldspar weathering [24]. The Na⁺ contents in all samples meet grade III of the groundwater quality standard limits of the People’s Republic of China. In this study area, the Mg²⁺ and K⁺ content varied from 9.68 to 97 mg/L and 0.36 to 23.6 mg/L.

Over the Hutuo River Drinking Area, the order of anionic dominance in the groundwater is HCO₃⁻ > SO₄²⁻ > Cl⁻ > NO₃⁻ > F⁻ > NO₂⁻. HCO₃⁻ is the dominant anion, varying from 186 to 578 mg/L, with an average of 186 mg/L. SO₄²⁻ ranges from 11 to 552 mg/L, with a mean concentration of 191.84 mg/L. The SO₄²⁻ contents in 20% of the samples surpass the permissible limit (250 mg/L). The Cl⁻ is from 8.98 to 404 mg/L (mean 72.54 mg/L), and the contents of Cl⁻ are more than its desirable limit (250 mg/L) in 75% of the total groundwater samples, which may cause a salty taste. The NO₃⁻-N is between 1.79 to 104 mg/L (mean 17.32 mg/L), and the proportion of NO₃⁻-N surpasses the permissible limit for grade III standards in the groundwater quality standard limits in 30.63% of the samples. Due to the highest standard-exceeding ratio of NO₃⁻, the source and health risk of NO₃⁻ should be investigated and analyzed further. The maximum, minimum, and average concentrations of F⁻ are 0.62, 0.05, and 0.26 mg/L, respectively, and all samples have concentrations lower than the standard limits.

3.2. Factors Affecting the Groundwater Chemistry

The Piper diagram is a widely used graphical tool for recognizing groundwater chemistry reactions and the evolution of groundwater [30,31]. The Piper diagram contains three main areas, and the cation and anion proportions of groundwater are plotted to evaluate the different types of the samples. As shown in Figure 2, the groundwater sample points in the Hutuo River Drinking Water Source Area are mainly distributed in Zone 1, Zone 2, and Zone 3. The results suggest that the groundwater belongs to the Ca-HCO₃ (78.1%), mixed Ca-Mg-Cl (20%), and Ca-Cl (1.9%) classifications. The anions and cations of groundwater samples are primarily concentrated in Zone E and Zone A, demonstrating that the dominant anions and cations detected over the study area are HCO₃⁻ + CO₃²⁻ and Ca²⁺, respectively. The results suggest that carbonate mineral weathering (such as calcite and dolomite) may be the main factor controlling groundwater chemistry in the Hutuo River Drinking Water Source Area. A total of 78.1% of the samples are classified as the HCO₃ water type, indicating the increased possibility of the ion exchange process, silicates, and carbonates weathering in groundwater. The other groundwater samples are classified as the Cl-water type, which implies evaporated dissolution and anthropogenic inputs in groundwater. Alkaline earth metals (Ca²⁺ and Mg²⁺) are the most important for most groundwater samples instead of alkaline metals (Na⁺ and K⁺); the high concentration of alkaline earth metals may be due to dolomite weathering. Samples clustered in Zone 1, Zone 2, Zone E, and Zone B illustrate the dominant role of carbonate and silicated weathering in the hydrochemistry of groundwater [32].

Except for the impact of rock weathering, the hydrochemistry of groundwater is easily affected by climate factors. The Gibbs diagrams are divided into three parts; groundwater samples located in three regions represent different evolution processes of groundwater, including rock, precipitation, and evaporation dominance [33]. Apart from one sample, most of the groundwater samples concentrate in the rock dominance area (Figure 3), suggesting that water–rock interaction is the dominant factor and influences the formation of groundwater hydrochemistry. As shown in Figure 3a, one groundwater sample is located in the evaporation dominance area, indicating that this groundwater sample is controlled by the evaporation factor. The evaporation process would upsurge salinity by increasing the content of Na⁺ and Cl⁻, and TDS would be intensified subsequently.

Reactions between groundwater and the aquifer media, such as rock weathering, evaporation, and ion exchange, would affect the hydrochemistry properties of groundwater significantly, and can be used for identification of the source of groundwater solutes. Several scatter plots are used to identify these reactions. As shown in Figure 4a, most of the samples plot along a 1:1 line for the bivariate diagram of Na⁺ and Cl⁻, which indicates that Na⁺ may originate from the dissolution of halite [27]. The halite rock might be a prime loading source of Cl⁻ due to the clustering of groundwater samples above the dissolution line (1:1), whereas the deviation of the sample points toward the Na⁺ axis also suggests that there are alternative sources of Na⁺, such as ion exchange and silicate rock weathering [34].

As shown in Figure 4b, the groundwater samples are mainly clustered above the y = x relationship line, which indicates that the dissolution of gypsum is not the main origin of Ca²⁺ and SO₄²⁻ [35]. In a plot of Ca²⁺ versus HCO₃⁻ (Figure 4c), only seven groundwater sample points fall within the 1:1 and 1:2 theoretical lines. Some of the points are located along the 1:1 line, proving that the dissolution of carbonated rocks is one of the Ca²⁺ sources [36]. Most of the points are located above the 1:1 line, which indicates multiple origins of Ca²⁺. The excess of Ca²⁺ over HCO₃⁻ indicates that the dissolution of gypsum might increase the concentration of Ca²⁺ in groundwater.

As shown in Figure 4d, some of the sample points scatter along the 1:1 line, which shows that the dissolution of calcite, dolomite, anhydrite, and gypsum are the dominant processes that affect the hydrochemistry of the groundwater [37]. The majority of the points are clustered above the equiline; the dominance of Ca²⁺ + Mg²⁺ over HCO₃⁻ + SO₄²⁻ can be an indicator of reverse ion exchange [38]. The phenomenon of cation exchange in the groundwater is further described by the negative slope of the trendline on the interionic plot Na⁺ + K⁺ − Cl⁻ vs. (Ca²⁺ + Mg²⁺) − (HCO₃⁻ + SO₄²⁻) [24,39] (Figure 4e). The scattering of sample points not only demonstrates the loading of anthropogenic input in groundwater but also indicates the presence of reverse ion exchange, which is predicted by (Ca²⁺ + Mg²⁺) versus (HCO₃⁻ + SO₄²⁻) [40].

3.3. Principal Components Analysis Results

Principal components analysis (PCA) is utilized to clarify the components that control the groundwater chemistry characteristics. Principal components (PCs) are calculated from the seventh parameter. The Kaiser–Meyer–Olkin (KMO) value is 0.705, and the significance value of Bartlett’s sphericity test is lower than 0.001. As shown in Figure 5, five PCs with eigenvalues > 1 explain 74.67% of the total variance in the original dataset. The results reflect the correlation between parameters and PCs, which are divided into three parts according to their absolute values: strong, medium, and weak, with values > 0.75, 0.75–0.5, and 0.5–0.3, respectively [41]. The parameters can be interpreted by each PC, and each PV has a geochemical understanding of the original datum.

The Pearson correlation coefficient is introduced to quantify the relationship between the chemical parameters (Figure 6). The correlation coefficient of 1 indicates a good positive correlation, a perfect negative relation between two parameters is implied by −1, while zero suggests no relationship between two parameters [19].

Principal component 1 (PC1) is dominated by TDS, TH, SO₄²⁻, Cl⁻, NO₃⁻, Ca²⁺, and Mg²⁺ (loadings between 0.78 and 0.99), and negatively correlated with pH (loading is −0.54). Thus, PC1 is considered as a salinity factor. As shown in Figure 6, TDS is positively correlated with Na⁺, Ca²⁺, Mg²⁺, SO₄²⁻, Cl⁻, and NO₃⁻; thus the variation of TDS in groundwater can reflect the regional impact of the salinity parameter and the corresponding modification [42]. Salinity is directly impacted by the contents of Na⁺, Ca²⁺, Mg²⁺, SO₄⁻, and Cl⁻; the ions are contributed by rock–water interaction, especially the dissolution of halite, carbonated rocks, and silicate rocks as described above.

Among the 160 groundwater samples, there are 49 samples with a concentration of NO₃⁻ higher than the maximum permissible limit of the groundwater quality standard grade III limits of the People’s Republic of China (20 mg/L). Nitrogen is of great significance in the biogeochemical cycle. Nitrate contamination is widespread in China, and the residents are exposed to the risk of high nitrate concentration in groundwater [43]. The source identification of NO₃⁻ can facilitate the improvement in groundwater quality, such as reduction in the usage of chemical fertilizers, improvement in the treatment processes of wastewater, and the remediation of the contaminated groundwater [44]. The nitrate in groundwater may be from multiple natural factors and anthropogenic activities, but it is difficult to quantify nitrate sources in groundwater [45]. The correlation between NO₃⁻/Na⁺ and Cl⁻/Na⁺ makes a distinction of nitrate sources between agricultural activities and urban sewage; different NO₃⁻ sources have different NO₃⁻/ Cl⁻ ratios [23]. As shown in Figure 7, the values of NO₃⁻/ Cl⁻ vary from 0.002 to 0.38; the low NO₃⁻/ Cl⁻ and elevated Cl⁻ suggest that NO₃⁻ in groundwater is significantly affected by the combination of both. Agricultural activities play the dominant role in the hydrochemistry formation process of groundwater [46]. A combination of agricultural components and communal effluent is in accordance with the dense population and farmland in the study area. The usage of agricultural fertilizer should be controlled. Thus, rock–water interaction and agricultural return control the PC1.

PC2 is distinguished by the reduced species Fe²⁺ and NO₂⁻, which may indicate a redox environment. Fe enrichment in groundwater usually indicates the reducing condition, where denitrification is inhibited [47]. PC3 shows maximum loading for Mn²⁺ (0.609) and F⁻ (0.498). It is reported that the dissolution of F-bearing carbonate mineral and Mn-hydroxides are the origin of F⁻ in groundwater [48]; the F⁻ and Mn²⁺ in groundwater mainly originate from geogenic sources [49].

PC4 is dominated by K⁺ (with a loading of 0.545). The site investigation indicates that the Hutuo River Drinking Water Source Area is located on the North China Plain, where agricultural activities are intensive and fertilizer is over-used. Fertilization with KNO₃ and NaNO₃ leads to deterioration of groundwater quality, and K⁺ is frequently detected with Na⁺ and other ions in groundwater [50,51]. The correlation of K⁺ and Na⁺ (p < 0.01) shown in Figure 6 verifies the utilization of agricultural fertilizer (Figure 6).

PC5 shows maximum loadings for Zn²⁺ (0.709) and Al³⁺ (0.416), and it is noted that both of them are not significantly correlated with other parameters (Figure 6). Therefore, the increase in these metals may be attributed to the aluminum silicate weathering and dissolution of carbonates (i.e., Smithsonite) [52]. The agricultural pollution sources may cause serious pollution to regional groundwater, and the exceeding of several water quality parameters indicates that the groundwater quality in the Hutuo River Drinking Water Source Area needs appropriate assessment.

3.4. Groundwater Quality Assessment

To further analyze the contributing parameters in the geochemical composition and their corresponding entropy weights, 14 parameters with different entropy weights and concentrations are employed to calculate the EWQI value. The entropy weights (w_j) and information entropy (e_j) values for the qualitative classification are provided in Table S1; the parameter with a higher entropy value would have a greater influence on groundwater quality. According to the calculated results, Fe²⁺ and NO₂⁻ have the highest weights of 0.28 and 0.26, respectively, while pH shows the lowest weight of 0.004. The EWQI results revealed that 97.5%, 1.88%, and 0.63% of the samples are classified as excellent, good, and fair, respectively (Figure 8).

The evaluation of different parameters indicates that the components of some groundwater samples are higher than grade III of the groundwater quality standard limits of the People’s Republic of China. As shown in Table 1, the TH values of 71.25% of the samples exceed the limit, and the NO₃⁻ values for 30.63% of the samples are higher than the limit. The EWQI calculations show that 99.37% of the samples are classified into excellent and good quality (grades I and II), indicating that the quality of groundwater in the Hutuo River Drinking Water Source Area is good and suitable for drinking [23]. These results demonstrate that only using limited parameters cannot estimate the real groundwater quality comprehensively.

To estimate whether the groundwater is ideal for agricultural irrigation in the Hutuo River Drinking Water Source Area, the sodium adsorption ratio (SAR), residual sodium carbonate (RSC), and potential salinity (PS) are calculated. Groundwater with HCO₃⁻ concentration above 90 mg/L is not ideal for irrigation, as it would exaggerate the sodic condition of the soil [24].

The minimum and maximum values of the SAR are 0.24 and 3.01, respectively, and the average is 0.72. The SAR values of all the groundwater samples are evaluated as excellent. Therefore, the groundwater in this study has no sodium hazard for agricultural soil and would not affect the normal infiltration rate of water significantly after a long-term irrigation. The minimum and maximum values of the RSC are −26.38 and −0.18, respectively. Hence, the concentration of dissolved bicarbonates and carbonates is below the sum concentration of calcium and magnesium (Mg²⁺ + Ca²⁺). Groundwater with such a low RSC value would not form sodium carbonate and would not lead to salinization and consolidation in soil [53].

As shown in Figure 9, the minimum and maximum values for PS in groundwater samples are 0.37 and 17.00, respectively, and the average is 4.04. More than 70% of the samples have a PS value exceeding 3, which places them as conditional. A PS value of a groundwater sample of 17 is classified as not recommendable for irrigation. The presence of high salt concentration in irrigation groundwater would result in the accumulation of salt in soil, and limit water as well as air circulation in root zones, thereby reducing irrigation efficiency [21].

4. Conclusions

In this study, hydrogeological and multivariate analyses are used to characterize the distribution of groundwater hydrochemistry and associated controlling factors over the Hutuo River Drinking Water Source Area. The NO₃⁻ concentration of the samples lower than grade III of national standards is 30.63%. The TH of the 71.25% groundwater samples exceed the national limit. The Piper diagram indicates that the groundwater types belong to the Ca-HCO₃ (78.1%), mixed Ca-Mg-Cl (20%), and Ca-Cl (1.9%) classifications. In the majority of the samples, HCO₃ and alkaline earth metals (Ca²⁺ and Mg²⁺) are the main anions and cations, indicating the possibility of an ion exchange process, weathering of silicates, carbonates, and the dolomite in groundwater. Graphical and binary diagrams indicate that the water–rock interaction plays a crucial role that influences the groundwater hydrochemistry, including the dissolution of halite, gypsum, and carbonated rocks, the weathering of silicate rocks, and ion exchange dissolution. The principal component (PC) analysis transforms the chemical components into five PCs, which represent the rock–water interaction and agricultural return, redox environment, geogenic sources, the utilization of agricultural fertilizer, and the weathering of aluminum silicates and dissolution of carbonates, respectively. The groundwater in the Hutuo River Drinking Water Source Area is classified as good, but the high concentration of salinity should be further discussed when used as irrigation water. Hence, the high concentrations of salinity and nitrate need to be monitored, and a groundwater pollution warning system is suggested to be established on this basis. The study may provide scientific support for sustainable groundwater management and pollution protection in Shijiazhuang (North China Plain) and other similar places.