Investigated area is located southeast Dead Sea along the highlands (Figure 1). It comprises a large part of the south region of Jordan extended between Latitude 30˚15 to 30˚55 N and Longitude 35˚10 to 36˚50 E. It has a total area of about 5100 km² [19]. The area is characterized by low population density and major industries such as cement factory in Al-Tafila area, phosphate mines in Al-Hasa, Al-Abied areas and potash production in the west of investigated area. Besides wastewater treatment plants that treat around 4000 m³/day in Al-Tafila and Al-Karak governorates. The study area receives different types of pollutants such as anthropogenic remains of solid and liquid wastes, industrial liquid and solid wastes, fertilizers, pesticides and irrigation return flows. On the other hand, the rainfall is low in the area. Intensive farming activities started in the early 1980’s especially at Al-Shoubak area where large amounts of good quality freshwater are consumed for irrigation purposes and excessive amounts of pesticides and fertilizers were added to the soil [20].

Figure 1. Geological map of Jordan. The study area location is highlighted.

The difference between a wet season and arid, hot summer conditions is one of the most significant aspects of the Mediterranean climate found in the studied area. The study area’s center highlands get 350 mm of rainfall annually, whereas the southeastern desert and west side that borders the Wadi Araba escarpment receive less than 50 mm [19][21]. During the winter, snowfall is common in the highlands, which are located between 1000 and 1600 meters above sea level. In the Al-Shoubak region, which is 1365 meters above sea level, the maximum recorded annual snowfall is 35 cm, and the average number of snowy days is around five [22]. According to Al-Khashman and Jaradat [15] (2014), the potential for evaporation in the region varies from around 1788 mm/year in the Al-Shoubak area to 3467 mm/year in Ma’an area. While relative humidity varies from 40% to 80%, the study region’s sunlight hours range from 9.0 hours per day in Al-Shoubak to 9.8 hours per day on average in the Ma’an area [22].

Geological setting of the study area is characterized by rock outcroppings that range in age from the Cambrian period to the present day. The Kurnub Group is predominantly consisting of sandstone, primarily found along portions rift side such as Tafila, Karak, and Shoubak. While the lithology of this group is consistent across Jordan, it becomes slightly more terrestrial to the south and east of area [23]. Rainwater is primary source of GW recharge in area, it plays good recharging the entire catchment area and serving as the main exploitable water resource. Groundwater moves both eastward and westward toward the central region of Wadi Araba, where the Dead Sea to the north and the Red Sea to the south serve as the two base levels [24]. The lithological units in the area consist of sedimentary rocks with thicknesses ranging from 40 to 480 meters, including layers from the Cretaceous and Tertiary periods. These layers are consisting of chalky limestone with chert intercalations, marl, limestone, and chert [25] (Figure 1).

Groundwater serves as primary water source in area, primarily recharge by precipitation throughout the catchment. It serves as most heavily used and dependable water resources in many areas valued for its consistent availability and quality. In the study area, the primary aquifer system from the Cretaceous period comprises several subsystems:

1) Lower Aquifer Systems: These consist of sandstone (Kurnub Sandstone) and limestone from the Lower Cretaceous period. The Kurnub Sandstone aquifer is made up of massive, white, and multi-colored sandstone with a total thickness of approximately 300 meters [25][26]. Found primarily along the rift side of the study area, the Kurnub group is dominated by sandstone. It is well-cemented, friable, and highly permeable sequences make it an excellent aquifer, offering favorable conditions for water storage and movement.

2) Systems of middle aquifers made up of the Amman, Wadi Al-Sir, and Hummar hydraulic complexes, which make up the Upper Cretaceous rock units. The primary aquifers in this system are A₁/A₂, A₃, A₄, A₅/A₆, A₇/B₂, B₂, and B₄. The A₁/A₂ is a decent aquifer made up of marl limestone, dolomitic limestone, grey mudstone that contains plant remnants, and gypsum lamina [24][25]. The A₃ is regarded as a poor aquifer and is made up of strata of laminated fibrous and locally nodular gypsum interbedded with marl, limestone, and mudstone. The A₄ is made up of gray limestone, crystalline dolomite limestone, and a lot of micrite and chert nodules. When broken and reunited, this deposit is thought to be extremely permeable, creating an excellent aquifer [26]. Due to its high jointing nature, the A₅/A₆ formation consists of marly limestone and marl, interspersed comprises occasional layers of dolomitic limestone, dolomite, and limestone, which collectively constitute an excellent aquifer. One of the most significant GW reservoirs in area is A₇/B₂ formation, which consists of chalk, dolomite, and thin marly limestone interbedded with chert layers [26].

The volume-weighted averages of different physical and chemical characteristics, derived from the samples and analyzed statistically, are presented in Table 1.

Table 1. Statistical analysis of physical and chemical parameters of groundwater samples, n = 372 samples.

EC: Electrical conductivity; TH: Total hardness; TDS: Total dissolved solids; SAR: Sodium adsorption ratio; RSC: Residual sodium carbonate; SI: Saturation index; PI: Permeability Index.

The accuracy of the obtained parameter was demonstrated by the ratio of total ions [30]. It was found that the average total of cations was equivalent to that of the anions 0.85 ± 0.28. Additionally, a variance R² of 0.87 was achieved from the linear regression of the cation sum on the anion sum for the samples included in this study, indicating that data quality very good. Temperature measured in field which had a mean value of 20.18˚C ± 0.94, with temperatures recorded at 16.81˚C during the rainy season for Bir El Harir No.1 and 24.75˚C during the dry season for Hasa well No.21. The depth of the water sources was the main factor contributing to the temperature differences observed for each well in the study area [19].

The pH readings from the average sample sites during the rainy season ranged from 6.65 at Hasa well No. 12 to 8.25 at Oran well. In the dry season, the average pH was 7.82 ± 0.28, with Hasa No. 19 showing a pH of 7.20 and Bir El Harir at 7.88. The main reason for the differences in pH values across various wells was the increase in bicarbonate concentrations in water aquifers. Table 2 shows median pH levels of the water samples met the standards set by WHO [31] and JSMO (2015) regulations.

Table 2. Jordanian Standards and WHO guidelines for drinking water quality.

During the wet season, the electrical conductivity (EC) of the water at Bir El-Harir was measured at 518.10 µs/cm, while Umurg well No. 2 recorded a much higher value of 1220.70 µs/cm. The mean EC value was 765.00 ± 167.4 µs/cm at 25˚C, with variations in the dry season ranging from 460 µs/cm in Fujaj well No. 4 to 1920 µs/cm in Umurg well No. 2. The high conductivity measured in samples from wells in Al-Tafila area corresponded to highest levels of major ions, likely due to ion exchange and the dissolution of minerals in aquifer [29][33]. The measured electrical conductivity (EC) values are slightly higher than the guideline value recommended by the World Health Organization (WHO) (400 µS/cm). The elevated EC observed in the groundwater samples is primarily attributed to the increased concentrations of major dissolved ions, including Ca²⁺, Mg²⁺, HCO 3 − , and SO 4 2 − . These ions originate predominantly from water-rock interactions, particularly mineral dissolution and ion-exchange processes occurring within the aquifer system. The average calcium concentration across the different wells was 83.77 ± 19.00 mg/L, with values varied from 52.30 mg/L to 149.20 mg/L. Notably, highest concentration was recorded in winter, attributed to precipitation that allowed calcium to leach from carbonate rocks and soil materials into the groundwater [34]. There was no significant difference in calcium levels between samples collected during the wet and dry seasons. The elevated calcium levels at Quaternary aquifer were linked to overexploitation.

The water samples showed average salinity levels of 28.53 ± 5.31 mg/L—as indicated from major ionic values such as Ca²⁺, with a range from 15.00 mg/L at the Q’A Ma’an 1 well to 40.15 mg/L at the Tahouneh 1 well. The summer measurements were particularly informative. Major ions present in GW samples show similar trend in their distribution (increase in summer and decrease in wet seasons). The increase in salinity content during summer is primarily due to agricultural water use and reuse. In contrast, the decrease in salinity levels during the dry and wet seasons suggests that rainfall has diluted groundwater (Figure 2). The reduction in salinity concentrations from the dry to rainy seasons indicates that rainfall has effectively diluted the groundwater. When comparing the contribution of sodium ions to that of calcium and magnesium, it is relatively minor.

Figure 2. Monthly mean value of Ca²⁺ ionic values in GW samples.

Mercado [23] and Al-Khashman [20] suggest that the reduced Na⁺:Cl⁻ ratio in water samples is due to interactions with clay minerals, which swap sodium for calcium and magnesium ions near groundwater outflows. The median Na⁺:Cl⁻ ratio recorded was 1. The composition of the aquifer, consisting of alternating layers of marl and limestone, further supports this idea, as the clay in the marl likely acts as the exchange medium. The average bicarbonate concentration in the water samples was 197.66 ± 48.41 mg/L, with values ranging from 119.90 mg/L in the Q’A Ma’an 1 well to 321.06 mg/L in the Tahouneh1 well. There was a noticeable increase in Cl⁻, K⁺, Na⁺, NO 3 − , and HCO 3 − from the summer to winter season. The levels of potassium, fluoride, and bromide were all significantly below the allowable limits. A common method for evaluating the relationship between two variables is the relationship. The statistical analysis revealed that Ca²⁺ has a strong positive correlation with Mg²⁺, Cl⁻, and SO 4 2 − (R² = 0.813, 0.740, and 0.741, respectively) with p < 0.01. In contrast, sodium showed a positive relationship both Cl⁻ and SO 4 2 − with (R² = 0.729 and 0.691) with p < 0.01, while Mg²⁺ demonstrated a significant strong correlation with Cl⁻ and SO 4 2 − (R² = 0.832 and 0.744). Additionally, Cl⁻ ions showed a greater affinity for HCO 3 − and SO 4 2 − with (R² = 0.837 and 0.824) with p < 0.01.

Water chemistry is influenced by interactions between groundwater and the minerals and dissolved gases present within the aquifer through processes such as mineral dissolution and precipitation [35]. To evaluate mineral-water equilibrium, the saturation index (SI) is commonly used. According to Aghazadeh and Mogaddam [36], the saturation index is calculated using Equation (1):

SI = log(IAP/Kt) (1)

where, K is the equilibrium solubility product of a mineral at a given temperature, and IAP is the ion activity product of the dissolved species in solution. The saturation index indicates the equilibrium state between groundwater and a mineral. An SI value of 0 indicates equilibrium (saturation), SI < 0 indicates undersaturation and a tendencyformineral dissolution, whereas SI > 0 indicates supersaturation and a tendency for mineral precipitation [20][35][37]. A summary of the saturation index statistics for the groundwater samples is presented in Table 1. Calcite and dolomite exhibited positive (or near-zero, if applicable) saturation indices, indicating that the groundwater is at or above equilibrium with these carbonate minerals and that precipitation is thermodynamically favored. In contrast, gypsum and anhydrite showed negative saturation indices in all samples, indicating that the groundwater is undersaturated with respect to these minerals and that they tend to dissolve rather than precipitate if present. These results suggest that carbonate mineral equilibria largely control the groundwater chemistry, whereas sulfate minerals remain undersaturated. The trilinear diagram developed by Piper (1953) illustrates the ionic composition of the groundwater samples, while the classification of Langguth (1966) (Figure 3) aids in hydrochemical interpretation. The groundwater samples were classified as alkaline earth waters dominated by bicarbonate or as alkaline earth waters containing both bicarbonate and chloride. Based on the hydrochemical composition, the dominant ions are sodium, potassium, magnesium, bicarbonate, chloride, sulfate, nitrate, phosphate, fluoride, and calcium. Overall, the groundwater chemistry is primarily controlled by the dissolution of carbonate rocks and is characteristic of freshwater conditions.

Chemistry of water is influenced by interacts with ions and dissolved gases present within the aquifer due to processes such as mineral precipitation and dissolution [35]. To evaluate the mineral-water balance, saturation indicators are utilized. Aghazadeh and Mogaddam [36] propose that Equation (1) can be used to determine saturation index of mineral.

The potassium level reflects the equilibrium solubility product of a compound at a specific temperature, whereas the ion activity product (IAP) describes the effective activity of the dissolved ionic species present in the solution. Minerals will dissolve when the saturation index (SI) is less than 1 and will precipitate when SI is greater than 1 [20]. The saturation index can be used to indicate the concentration levels of minerals present in the analyzed water samples. Specifically, when saturation index is less than 1, minerals dissolve, and when SI is greater than 1, they precipitate [35][37]. A summary of the saturation index statistics for the water samples is presented in Table 1. Calcite and dolomite were present in all groundwater samples, while the indices for gypsum and anhydrate were negative across all samples. This suggests that the water samples below the saturation limit for gypsum and anhydrate may contain higher levels of dissolved gypsum and anhydrate.

The trilinear diagram created by Piper in 1953 illustrated the ion proportions in groundwater samples, while Langguth’s classification from 1966 (Figure 3) helped interpret the results. The water samples were categorized as alkaline earth waters high in bicarbonate, or as alkaline earth waters content in both bicarbonate and chloride. Based on the water sample chemistry, the ionic ratios ranked from highest to lowest are sodium, potassium, magnesium, bicarbonate, chloride, sulfate, nitrates, phosphate, fluoride, and calcium. The water’s chemistry is mainly governed by the dissolution of carbonate rocks. Despite this, it is generally considered to have freshwater conditions.

Figure 3. Piper diagram of GW in studied area (values in % meq/L).

To assess drinking water quality, TDS and TH measurements are compared against JSMO [32] and WHO [31] guidelines (Table 2). Overall, the TDS levels in water parameters are within acceptable limits set by JSMO [32] and WHO [31]. Most GW samples were categorized as very hard water (Table 3), according to Sawyer and McCarty [38] for assessing their suitability of water samples for uses.

Table 3. Classification of the water samples on the basis of the total hardness.

Measured average hardness of water samples was 316.30 mg/L, ranging from 200.10 mg/L to 485.10 mg/L. Notably, Q’A Ma’an 1 well had the highest recorded value. The total hardness (TH) of drinking water can reach up to 500 mg/L, while the minimum acceptable level is 100 mg/L [31][39][40].

The average nitrate value was 80.05 ± 25.65 mg/L, varied from 28.10 mg/L to 132.10 mg/L. Elevated nitrate concentrations in the groundwater (GW) samples, particularly during the summer season, are primarily attributed to intensified agricultural activities, including the application of nitrogen-based fertilizers for irrigation, enhanced biological nitrogen fixation, and the infiltration of untreated domestic wastewater from cesspools widely distributed throughout the villages within the study area [15]. Despite these seasonal increases, only 3% of the analyzed groundwater samples exceeded the maximum permissible nitrate concentration of 50 mg/L established by the World Health Organization for drinking water, whereas approximately 95% of the samples remained within the recommended guideline value, indicating generally acceptable groundwater quality with respect to nitrate contamination. Fluoride is a key trace ion found in groundwater and can occur in substantial quantities because the bedrock contains fluoride-bearing minerals [25][40][41]. Groundwater samples exhibited an average fluoride level of 1.58 ± 0.84 mg/L, with individual measurement varying between 0.65 mg/L to 4.12 mg/L. The results indicate that the fluoride values in all water samples comply with Jordan’s drinking water standards and fall within the acceptable range.

Influence of GW ions and nutrient levels on plants and soil has is essential for evaluating irrigation suitability [5][6][13][42]. Amount of water assigned for agricultural uses depends on availability of water resources. Various parameters, including pH, EC, SAR, Sodium Percentage (SP), and RSC, are utilized to evaluate suitability of water for agricultural uses [40][43].

Electrical conductivity (EC), a proxy for TDS in GW, is a key indicator of salinity. Elevated salinity concentration in water used for irrigation lowers osmotic pressure in root zone, restricting water absorption and impairing plant growth [15][35][44]. In addition, EC is a useful tool for assessing water quality and provides a dependable measure of the salt threat to plants and crops. The EC values for the water samples varied between 518.10 µs/cm to 1220.70 µs/cm, with a mean of 765.00 ± 167.20 µs/cm. According to the results, nearly all water samples fell inside the acceptable permissible values for irrigation water quality [5][6][40][45]. The TDS levels showed value of 485.20 mg/L, between 313.25 mg/L to 749.41 mg/L that is below the suggested limit of 2000 mg/L, suggesting that GW are suitable for irrigation and not affected by osmotic pressure of soil solution [40][43]. The TDS value generally below the threshold set by JSMO [32]. The data showed that, excluding April, when TDS levels exceeded those of June, TDS values tended to rise during dry seasons compared to rainy ones.

The average boron content in samples was 0.21 mg/L, varied from 0.02 mg/L to 0.67 mg/L (Table 4). For semi-sensitive crops, all groundwater samples were below the allowable limits. Most vulnerable crops can tolerate only 0.5 - 1.0 mg/L, as noted by Todd [46]. The SAR is used as a key indicator to assess sodium threat on crops and GW suitability for agricultural use. The later parameter can be calculated by applying formula below [47].

SAR = Na⁺/(Ca²⁺ + Mg²⁺)^0.5/2 (2)

All values are expressed in meq/L.

Table 4. Permissible limits of boron in irrigation water for several types of crops.

Average value of SAR was 1.730, with a range from 0.33 to 1.95. The classification of low sodium (S1) applies to the 27 samples collected the area. Majority of these samples are categorized as C3S1, which signifies high salinity and low sodium risk, making them suitable for irrigation across nearly all soil types, based on the data plotted on the US salinity diagram [48] (Figure 4). All samples showed Na percentages below 40% (Figure 5), suggesting that the water is almost adapted to irrigation conditions [49]. RSC denotes the abundance of carbonate and bicarbonate [50]. The RSC is measured using Equation (3).

All values are present in meq/L.

The classification of irrigation water based on RSC values results is presented in Table 1. RSC is used to classify different types of water for agricultural purposes [1][4]. The mean RSC level was −2.49 ± 1.17, with a range from −5.19 meq/L to −1.65 meq/L. All samples showed satisfactory water quality, as RSC levels were below 1.25 meq/L.

Elevated HCO 3 − levels of irrigation water can lead to increased toxicity and negative impacts on plant nutrition. However, as discussed later, PI levels of the samples revealed their suitability for irrigation [45]. The PI value serves as an indicator of the appropriateness of irrigation water, assessing the salt hazards associated with it.

Figure 4. Rating of GW samples in relation to salinity (EC) and sodium hazard (SAR) based on USSL diagram.

The Permeability Index (PI) of the groundwater samples varied from 21.33 to 34.51, with a mean value of 29.83. The majority of the samples were distributed within Class I and Class II of the permeability index classification, reflecting favorable to moderately favorable conditions for irrigation use across the study area. Approximately 35% of the groundwater samples were categorized as good, while 63% were classified as suitable for irrigation, indicating that most groundwater resources possess acceptable permeability characteristics for sustained agricultural application [40][51].

Figure 5. Rating of GW samples on the basis of EC and Na% (after Wilcox [49]).

Historically, trace metals have been associated with both natural and human activities, and they can be found in surface water as well as groundwater. The two main natural processes that leads to the higher values of metals in water are chemical alteration of rocks and soil nutrient depletion [14][52]. The release of metals from soils and similar materials greatly affects their stability in water. Factors including co-precipitation, hydration, pH, and adsorption are all involved in this process [37][52]. Table 5 provides analytical evaluation of elemental values of samples. Across the majority of water samples trace metals values are relatively low, likely due to high pH (above 7.0) which either promotes metals concentration or inhibits leaching host rock [18][53]. The iron content in the water samples averaged 112.35 µg/L ± 42.29, having levels varied between 65.23 µg/L to 198.12 µg/L.

Groundwater contains low concentrations of iron because iron forms a strong bond with oxygen, which only break apart when there is no oxygen. The detected iron concentration in water was significantly lower than thresholds suggested by the WHO potable water. As presented in Table 5, lead content in samples varied between 10.00 µg/L to 54.10 µg/L, with a mean value of 24.53 µg/L. Based on JSMO [32], all tested samples fell within the permitted range and were under tolerance levels (0.05 mg/L).

Mean value of manganese (Mn) was 17.50 µg/L ± 4.96, with values between 8.10 µg/L and 24.80 µg/L. Nevertheless, every water samples had Mn concentrations that were below the acceptable threshold for drinking water quality. Zn levels varied from 9.50 µg/L to 41.00 µg/L, with a mean value of 23.56 µg/L ± 7.83. All groundwater samples contained zinc levels below the recommended threshold set by the Jordanian Standard (2001). Levels of other trace metals were also below levels considered safe for drinking.

Table 5. Statistical analysis of trace metals of groundwater samples.