Hydrogeochemical Characterization and Suitability Assessment of Groundwater: A Case Study in Central Sindh, Pakistan

Groundwater is the most important water resource, on which depends human geo-economic development and survival. Recent environmental changes and anthropogenic activities render groundwater severely vulnerable. Groundwater in Central Sindh, Pakistan, is facing a similar situation. Hydrogeochemical characteristics of the groundwater in the said region were investigated by analyzing 59 groundwater samples via agricultural and drinking indices, using various statistical methods and graphical approaches to identify factors affecting groundwater. Major reactions occurring in the groundwater system were quantified by hydrogeochemical modeling. A statistical summary reveals the abundance of cations is Na+ > Ca2+ > Mg2+ > K+, while the abundance of anions is HCO3− > Cl− > SO42. Groundwater chemistry is mainly of rock dominance. Correlation analysis and graphical relationships between ions reveal that ion exchange and rock weathering such as the dissolution of halite, albite, and dissolution of carbonate minerals are important rock–water interactions, governing the evolution of groundwater chemistry. Hydrochemical facies are predominantly of mixed CaMgCl and Na-Cl type, with few samples of Ca-HCO3 type, which constitutes fresh recharged water. Based on the Water Quality Index (WQI), 28.82% samples were found to be unsuitable for drinking. A United States Salinity Laboratory (USSL) diagram, Wilcox diagram, and other agricultural indices indicate that majority of the groundwater samples fall within the acceptable range for irrigation purposes.


Introduction
The importance of freshwater resources and its provision for every form of life is inevitable [1]. Being the elixir of life, water resources ensure the stability of the ecosystem and the status of human health [2]. Out of the total volume of water on Earth (i.e., 1600 × 10 6 km 3 ), approximately 3.0 × 10 6 km 3 of groundwater and 0.1 × 10 6 km 3 of surface water is available as freshwater resources, which is 0.1938% of the total volume of water [3]. These approximations compel us to take strict initiatives for preservation of the available water resources to ensure its continuous and adequate availability for all living beings [4]. The key risks to freshwater resources are over-exploitation and over-consumption [5]. Since water scarcity is prevalent around the globe [6,7], groundwater exploitation emerges as an alternative to fulfill elevating water demands [8,9].
The findings may facilitate a clear understanding to address the adverse effects, and the solution is advocating the groundwater quality at canal command level in Sindh province.

Location and Climate
The study area (Rohri canal command area) is located in the middle of the lower Indus plain and is one of the 14 annuls commonly called Canal Command Areas [42]. It stretches from longitudes 67 • 54 to 69 • 20 E and latitudes 24 • 44 N to 27 • 16 N covering an area of about 11,639 km 2 ( Figure 1). The climate of the area is mostly hot and dry, and can be categorized as an arid subtropical zone, i.e., hot in summer and cold in winter. The temperature rises to as high as 53 • C in summer, while in winter it drops to low as 2 • C [43]. The average annual precipitation is 260 mm [44]. The most cultivated crops in the area are wheat and cotton and are grown within the delta plain of Sindh and in the annually inundated lands [35].
The study area (Rohri canal command area) is located in the middle of the lower Indus plain and is one of the 14 annuls commonly called Canal Command Areas [42]. It stretches from longitudes 67°54' to 69°20' E and latitudes 24°44' N to 27°16' N covering an area of about 11,639 km 2 ( Figure 1). The climate of the area is mostly hot and dry, and can be categorized as an arid subtropical zone, i.e., hot in summer and cold in winter. The temperature rises to as high as 53 °C in summer, while in winter it drops to low as 2 °C [43]. The average annual precipitation is 260 mm [44]. The most cultivated crops in the area are wheat and cotton and are grown within the delta plain of Sindh and in the annually inundated lands [35].

Geology and Hydrogeology
The area has a rough topography, and the land slope is 0.000095 from north to south. Soils are generally coarse in texture along former meander floodplains, whereas the soil texture is smoother and finer across the flooded cover plain. The area is covered mostly by meander floodplains and consists of bar deposits, channel in-fills and channel scars ( Figure 1). Fine-textured soils constitute 36% of the area and the medium soil constitute 60%. Soil surface salinity occurs in small scattered patches throughout the research area [45]. The primary reason of prevalent salinization in the area is under-watering the crops, low cropping intensity, and seepage from canals and lateral channels. Chemical analysis reveals that almost 15% of the land under study is moderate-to-highly saline with saline-alkali land constituting over 5.5% of the total land mass [46].

Geology and Hydrogeology
The area has a rough topography, and the land slope is 0.000095 from north to south. Soils are generally coarse in texture along former meander floodplains, whereas the soil texture is smoother and finer across the flooded cover plain. The area is covered mostly by meander floodplains and consists of bar deposits, channel in-fills and channel scars ( Figure 1). Fine-textured soils constitute 36% of the area and the medium soil constitute 60%. Soil surface salinity occurs in small scattered patches throughout the research area [45]. The primary reason of prevalent salinization in the area is under-watering the crops, low cropping intensity, and seepage from canals and lateral channels. Chemical analysis reveals that almost 15% of the land under study is moderate-to-highly saline with saline-alkali land constituting over 5.5% of the total land mass [46]. Quaternary sediments are a dominant feature of the geology of the area, which can often be hundreds of meters thick. Lithological studies indicate that there is a 200 to 400 feet thick sandy layer present below the surface. They are well sorted, fine to medium micaceous sands with bands and lenses of silt and silty clay [35]. The deposits are extremely variable, and the variation in lithology is so intense that it is difficult to correlate the strata found in two adjacent boreholes. However, the relative percentage of sand and clay bands is remarkably constant over large areas. The depth to water table variates from 1.56 m to 11.93 m in this aquifer with an average depth of 4.53 m. The direction of groundwater flow is defined by the individual measurement of hydraulic head which are combined to obtain the contour maps of the water level ( Figure 1). The hydraulic heads in the current study area range from 10m to 28 m. In upper part, the flow direction is more south westward, while in middle and lower part, the flow direction is west ward, more toward and along river Indus. Sand is generally the predominant material making a fairly unified, transmissive and non-artesian aquifer. Groundwater yields from these sediments are typically around 50-300 m 3 /h. The storage factor is about 0.2 and transmissibility is 2.58 cm 2 /s. Vertical permeabilities are low in comparison to lateral ones but are just enough to ensure that there is a transmission of recharge from layer to layer [47].

Sample Collection and Analysis
In order to assess the groundwater quality of the Rohri canal command area, a total of 59 groundwater samples were collected from wells, boreholes, and hand-pumps. Before sampling, wells were pumped for several minutes to avoid the effects of stagnant water. Samples were then stored in rinsed and properly washed 2.5 L glass bottles. These samples were then analyzed in the standard water quality laboratory of the Pakistan Council of Research in Water Resources (PCRWR). A pH meter and electrochemical analyzer (Hac 44600-00, Loveland, CO, USA) were used to measure the pH, electrical conductivity (EC), and total dissolved solid (TDS). An ultraviolet-visible (UV-VIS) spectrophotometer (Analytik Jena, Jena, Germany) was used to analyze samples for major anions, i.e., nitrate (NO 3 -N) and sulfate (SO 4 2− ), while titration method was employed to analyze chloride (Cl − ) and bicarbonates (HCO 3 − ) [48]. To measure major cations like Na + , K + , and Fe 2+ , a Flame photometer (PFP7, Cambridgeshire, UK) was used. Volumetric titration with ethylene diamine tetra acetic acid (EDTA, 0.05 N) with <2% analytical error was used to analyze Ca 2+ and Mg 2+ . Total alkalinity in the samples was measured by acid titration using methyl-orange. Atomic absorption spectrophotometer (AAS Vario 6 Analytik Jena, Jena, Germany) was used to determine arsenic.
To validate the quality of water analyses, charge balance error (CBE) was computed. Water samples having a higher concentration of cations show positive CBE, while negative CBE is credited to higher concentrations of anions [49]. CBE was computed by Equation (1); where ionic concentrations are expressed in milliequivalent per liter (meq/L). According to the standard protocols, only those water samples were accepted that had less than ±5% CBE [50]. The Water Quality Index (WQI) values were computed to assess the suitability of groundwater for drinking purposes [51]. Three computing steps calculate WQI: 1.
The first step involves the assignment of weight (w i ) to each of the nine parameters (pH, TDS, Na, Mg, Ca, Cl, SO 4 , HCO 3, and K) based on their relative importance to the overall quality of groundwater (Table 1). Total dissolved solids, chloride and sulfate are given a maximum weight of 5 due to their significant role in assessment, while bicarbonate is given a minimum weight of 1 because of its insignificant importance. The other parameters (pH, Na, Mg, Ca and K) are assigned weights between 1 and 5 based on their significant role while assessing the evaluation of groundwater quality. 2. The second step involves the computation of relative weight (W i ) of each parameter (Equation (2)).
where W i is the relative weight, w i− is the weight of each parameter and n is the number of parameters.

3.
The third step is based on computation of the quality rating scale (qi) for each parameter (Equation (3)).
where q i is the quality rating, C i is the concentration of each parameter in mg/L, and S i is the WHO standard for each parameter in mg/L ( Table 1). The sub-index (SI) for each parameter is first calculated (Equation (4)) for the computation of WQI which requires the summation of sub-indices of all parameters in each sample (Equation (5)).
where SI i and W i is the sub-index and relative weight of the ith parameter, while qi is the rating based on the concentration of ith parameter. For evaluating suitability for irrigation purposes, some commonly used indices like the sodium absorption ratio (SAR), residual sodium carbonate (RSC), sodium percentage (Na%), permeability index (PI), magnesium hazard (MH), Kelley's ratio (KR) and potential salinity (PS) were computed [52]. Summary of the indices has been presented in Table 2.

Statistical Data Analysis
Statistical analyses play a pivotal role in interpreting the data set by representing various operations [53]. Regression along with Pearson correlation analysis was performed in SPSS (v23, SPSS Inc, Armonk, NY, USA) to delineate the relationships among water quality parameters. Piper diagram was prepared through Aqua-Chem (version 2010.1, Waterloo Hydrolgeologic, Kitchner, Ontario, Canada) to interpret hydrochemical facies. Saturation indices were calculated through geochemical modeling program PHREEQC (version 3.1) which determine the tendency of groundwater to dissolve or precipitate a particular mineral [54].

Hydrochemical Parameters Statistics
Hydrochemical parameters were computed in accordance with WHO protocols [55]. Table 3 presents the statistical summary of analyzed hydrochemical parameters. The value of turbidity ranges from 0 to 165 NTU (Nephelometric Turbidity Units) with a mean value of 7.82, which is relatively elevated. The high turbidity is due shallow and poorly built wells [56]. The pH value varies from 6.5-8.2 having a mean value of 7.41, depicting neutral to slightly alkaline nature of groundwater. The mean values of EC, total dissolved solids (TDS), and total hardness (TH) are 1570.97 µS/cm, 993.92 mg/L, and 421.12 mg/L respectively, and is higher than the WHO standard apart from TDS. Dissolution of minerals and soluble salts, and evaporation of shallow groundwater are the contributing factors of elevated salinity across the study area [46]. The concentration of Na + and K + ranges from 17 mg/L to 638 mg/L and 0 to 25 mg/L, with average values of 165.20 mg/L and 3.53 mg/L, respectively. Mainly, the dissolution of minerals containing Na + and K + with surrounding rocks leads to higher concentrations [57]. Ca 2+ and Mg 2+ vary from 14 mg/L to 220 mg/L and 10 mg/L to 175 mg/L respectively, with mean values of 76.46 mg/L and 55.41 mg/L, which are mainly due to carbonate minerals. The concentration of HCO 3 − ranges from 59 mg/L to 950 mg/L, with an average concentration of 308.90 mg/L. SO 4 2− and Cl − varies from 20 mg/L to 600 mg/L and 16 mg/L to 779 mg/L respectively, with a mean values of 169.88 mg/L and 209.76 mg/L. Dissolution of gypsum, sulfate-bearing minerals and halite cause this rise in concentration [58]. According to the descriptive statistics of hydrochemical parameters, the abundance of cations is Na + > Ca 2+ > Mg 2+ , while the abundance of anions is HCO 3 Fluoride concentration varies from 0 mg/L to 2.0 mg/L with an average value of 0.42 mg/L, while most of the samples are in the permissible limits. Fluoride concentration in its extreme ranges portrays adverse effects on human health [59]. The value of NO 3 -N ranges from 0 mg/L to 9.90 mg/L having a mean value of 0.94 mg/L. The higher concentration of NO 3 -N is attributed to the excessive use of fertilizer and irrigation by wastewater but in the study area, all the samples have been found to be in the acceptable range. The concentration of Fe varies from 0 mg/L to 1 mg/L having a mean value of 0.09 mg/L.
Arsenic concentration in the research area ranges between 0 µg/L to 250 µg/L, while 15 (25.42%) samples were beyond the permissible range (10 µg/L). Elevated concentration of As in groundwater as a consequence of natural or anthropogenic sources has become a major environmental concern [60]. Climatic and geogenic sources have resulted in the varying concentration of As in groundwater, which is mainly because of moderately saline, alkalinity, and anoxic conditions [61]. It is agreed that groundwater contaminated with geogenic arsenic is more profound in alluvial aquifers [62,63]. The primary composition of these alluvial aquifers is sandstone, sand, silt, and gravel that remain in a flood plain or river channel over a longer period of time. The aquifer of the lower Indus is of similar composition [64]. As compared to other parts of the country, arsenic poisoning in the lower Indus is rather high [65], which is causing adverse effects on human health [66]. Natural mobilization of arsenic in groundwater is enhanced because of the pH-based reductive dissolution of iron hydroxide (FeOH) and competitive sorption of bicarbonate minerals in the presence of microorganisms along with evaporative enrichment. The anthropogenic causes of arsenic enrichment include water logging, coal-mining, and excessive use of pesticides [64].

Hydrochemical Facies
Hydrochemical facies depict the overall scenario of the interaction of groundwater solutions within a lithological structure. They are quite beneficial in interpreting the groundwater transition and pattern of its flow [67]. Piper diagram [68] presents a comprehensive graphical representation of the hydrochemistry of samples and their hydrochemical regimes.
In order to elucidate the chemical differences, all the samples were plotted in a piper diagram ( Figure 2). Most of the samples fall in Zone 4 (mixed CaMgCl type) and Zone 2 (NaCl type), where the rock-water interaction significantly interprets hydrochemical behavior, anthropogenic activities, interaction with the unsaturated zone, increased resident time, ion exchange and reverse ion exchange. Few samples lie in Zone 1 (CaHCO 3 type), constituting fresh recharged water. With respect to cations, groundwater samples fall in Zone D (Na + K type) and Zone B (mixed type), depicting the prominence of silicate weathering and ion exchange. With respect to anions, most of the samples fall in Zone E (HCO 3 type) and Zone B (mixed type), while few samples fall in Zone G (Cl type), representing the dominance of carbonate weathering and dissolution of evaporite while the dissolution of gypsum is minimal.
exchange. Few samples lie in Zone 1 (CaHCO3 type), constituting fresh recharged water. With respect to cations, groundwater samples fall in Zone D (Na + K type) and Zone B (mixed type), depicting the prominence of silicate weathering and ion exchange. With respect to anions, most of the samples fall in Zone E (HCO3 type) and Zone B (mixed type), while few samples fall in Zone G (Cl type), representing the dominance of carbonate weathering and dissolution of evaporite while the dissolution of gypsum is minimal.

Correlation Analysis
According to the Pearson correlation matrix ( The association between TDS and major constituent ions is beneficial in explaining the hydrochemical processes. TDS has been found to be strongly correlated with Na + (0.92), Ca 2+   weathering except the dissolution of halite and mirabilite, while the strong correlation of HCO3 − with Ca 2+ (0.80) and Mg 2+ (0.77) illustrate the dissolution of carbonate minerals (calcite and dolomite). A strong correlation between Ca 2+ and SO4 2− (0.73) suggests the dissolution of gypsum. The association between TDS and major constituent ions is beneficial in explaining the hydrochemical processes. TDS has been found to be strongly correlated with Na + (0.92), Ca 2+ (0.86), Cl − (0.94), Mg 2+ (0.84), SO4 2− (0.90) and HCO3 − (0.86). All the ionic concentrations increase with the increase in TDS value (Figure 3).

Silicate Weathering
The contribution of silicate weathering plays a pivotal role in controlling the major ion chemistry of groundwater [69]. It is hard to quantify the silicate weathering products due to the incongruent nature of degradation of silicates, which yields a variety of solid phases (mostly clays) with other dissolved species [70]. Sodium which is the most abundant cation in the study area is derived from silicate weathering and by the dissolution of halite. If halite dissolution is the sole source of sodium (Equation 6), then the molar ratio of Na + /Cl − would be equal to one, while the deviation from 1:1 line

Silicate Weathering
The contribution of silicate weathering plays a pivotal role in controlling the major ion chemistry of groundwater [69]. It is hard to quantify the silicate weathering products due to the incongruent nature of degradation of silicates, which yields a variety of solid phases (mostly clays) with other dissolved species [70]. Sodium which is the most abundant cation in the study area is derived from silicate weathering and by the dissolution of halite. If halite dissolution is the sole source of sodium (Equation 6), then the molar ratio of Na + /Cl − would be equal to one, while the deviation from 1:1 line (Figure 4a) is attributed to the contribution of silicate weathering and ion exchange, e.g., the dissolution of albite (Equation (7)) might be responsible for the increment of Na + in groundwater.  This fact is well supported by the saturation index of halite, which is under saturated with respect to water ( Figure 5). This fact is well supported by the saturation index of halite, which is under saturated with respect to water ( Figure 5). NaCl → Na + + Cl − .  NaCl → Na + Cl .
The influence of silicate weathering and carbonate dissolution is further illustrated by Nanormalized Ca 2+ versus Mg 2+ plot ( Figure 6a) and Na-normalized Ca 2+ versus HCO3 − plot (Figure 6b). The Na-normalized Ca 2+ versus Mg 2+ plot shows that most of the Mg 2+ is derived from carbonate dissolution except the silicate weathering, while Na-normalized Ca 2+ versus HCO3 − plot demonstrates that samples tend to fall close to silicate weathering rather than carbonate and evaporite dissolution [71]. If silicate weathering is a prominent source of sodium, then the most abundant anion should be HCO3 − [72]. The abundance of bicarbonate among anions justifies this statement. The estimation of the ratio between Na + and total cations (TZ + ) would be helpful in understanding silicate weathering (Figure 4b). The majority of the samples fall near Na + = 0.5 TZ + line, which indicates the contribution of silicate weathering in the concentration of sodium in groundwater. The influence of silicate weathering and carbonate dissolution is further illustrated by Na-normalized Ca 2+ versus Mg 2+ plot ( Figure 6a) and Na-normalized Ca 2+ versus HCO 3 − plot ( Figure 6b). The Na-normalized Ca 2+ versus Mg 2+ plot shows that most of the Mg 2+ is derived from carbonate dissolution except the silicate weathering, while Na-normalized Ca 2+ versus HCO 3 − plot demonstrates that samples tend to fall close to silicate weathering rather than carbonate and evaporite dissolution [71]. NaCl → Na + Cl .
The influence of silicate weathering and carbonate dissolution is further illustrated by Nanormalized Ca 2+ versus Mg 2+ plot ( Figure 6a) and Na-normalized Ca 2+ versus HCO3 − plot (Figure 6b). The Na-normalized Ca 2+ versus Mg 2+ plot shows that most of the Mg 2+ is derived from carbonate dissolution except the silicate weathering, while Na-normalized Ca 2+ versus HCO3 − plot demonstrates that samples tend to fall close to silicate weathering rather than carbonate and evaporite dissolution [71]. If silicate weathering is a prominent source of sodium, then the most abundant anion should be HCO3 − [72]. The abundance of bicarbonate among anions justifies this statement. The estimation of the ratio between Na + and total cations (TZ + ) would be helpful in understanding silicate weathering (Figure 4b). The majority of the samples fall near Na + = 0.5 TZ + line, which indicates the contribution of silicate weathering in the concentration of sodium in groundwater. line indicate less contribution of Ca 2+ and Mg 2+ by the dissolution of carbonates. The oversaturation of calcite and dolomite with respect to water indicated by the saturation indices of these minerals proves this statement ( Figure 5).
According to Figure 4d, samples falling along the 1:1 line indicate the dissolution of gypsum as a contributor of Ca 2+ and SO 4 2− ions in groundwater (Equation (10)). Moreover, under-saturation of gypsum with respect to water ( Figure 5) allows it to dissolve in groundwater. However, samples falling below the equiline demonstrate the contribution of SO 4 2− by the dissolution of Glauber's salt (NaSO 4 ·10 H 2 O) (Equation (11)), which also elevates the concentrations of Na + ions in the groundwater.

Ion Exchange
Chloro-alkaline indices (CAI-1 and CAI-2) proposed by Schoeller [73] provide information about the ion exchange reactions, which have significant impacts on groundwater chemistry and its evolution [74,75]. The following formula can calculate the two indices: where concentrations are in meq/L. The direct ion exchange occurs when both indices give positive values expressed by Equation (14), while Equation (15) indicates the reverse ion exchange as a result of negative values of CAI-1 and CAI-2.
Ca 2+ + 2NaX → 2Na + + CaX 2 (15) where soil exchange is expressed by X [76]. The possible role of ion exchange in hydrochemistry and evolution of groundwater can be studied by bivariate diagram between (Figure 7b) (Na + + Cl − + K + ) and [(Ca 2+ + Mg 2+ ) -(SO 4 2− + HCO 3 − )] [77]. (Na + + Cl − + K + ) indicates the increment of Na + in the system by the processes other than halite dissolution, while [(Ca 2+ + Mg 2+ ) -(SO 4 2− + HCO 3 − )] represents the increment of cations Ca 2+ and Mg 2+ that are credited to processes excluding carbonate or silicate weathering (dissolution of gypsum, calcite, and dolomite) [78]. A linear relation between the parameters with slope equal to −1 indicates the significance of ion exchange as an important factor controlling the groundwater chemistry and its evolution [79]. According to Figure 7b, the relationship between parameters shows linearity with a slope value of −0.931 (Equation (16)), which is very close to the theoretical value of −1, indicating the ion exchange between Na + , Ca 2+ , and Mg 2+ .

Groundwater Chemistry Formation Mechanism
Groundwater resource development and quality protection require a better understanding of the key factors governing groundwater chemistry [75]. Gibbs (1970) proposed his well-known Gibbs diagram for studying groundwater chemistry formation mechanism. The two sub diagrams ( Figure  8a and 8b) include relationship of TDS with weight ratio of (Na + + K + ) versus (Na + + K + + Ca 2+ ) and TDS with weight ratio of Cl − versus (Cl − + HCO3 − ). According to Gibbs' diagram, three factors influence the groundwater chemistry, which include rock dominance, evaporation dominance and precipitation dominance [80,81]. According to Figure 8, most of the samples lie in the rock dominance zone, indicating that rock weathering is the primary source that controls the groundwater chemistry and its evolution. Parent rock weathering facilitates the process by which dissolvable salts and minerals become incorporated with groundwater. Moreover, long residence time of rock-water interaction also aids the mineral dissolution [57]. Figure 8 also shows that few samples fall in evaporation dominance zone. The influence of evaporation is attributed to the shallow groundwater depth (typically less than 3 m), which results in intense evaporation in the alluvial plain. Most of the samples are plotted in the lower left part of Figure 7a, indicating reverse ion exchange expressed by Equation (11), which leads to the increment of Na + and decrement of Ca 2+ in groundwater. However, few samples fall in the upper right part, which signify direct ion exchange (Equation (10)).

Groundwater Chemistry Formation Mechanism
Groundwater resource development and quality protection require a better understanding of the key factors governing groundwater chemistry [75]. Gibbs (1970) proposed his well-known Gibbs diagram for studying groundwater chemistry formation mechanism. The two sub diagrams (Figure 8a,b) include relationship of TDS with weight ratio of (Na + + K + ) versus (Na + + K + + Ca 2+ ) and TDS with weight ratio of Cl − versus (Cl − + HCO 3 − ). According to Gibbs' diagram, three factors influence the groundwater chemistry, which include rock dominance, evaporation dominance and precipitation dominance [80,81]. According to Figure 8, most of the samples lie in the rock dominance zone, indicating that rock weathering is the primary source that controls the groundwater chemistry and its evolution. Parent rock weathering facilitates the process by which dissolvable salts and minerals become incorporated with groundwater. Moreover, long residence time of rock-water interaction also aids the mineral dissolution [57]. Figure 8 also shows that few samples fall in evaporation dominance zone. The influence of evaporation is attributed to the shallow groundwater depth (typically less than 3 m), which results in intense evaporation in the alluvial plain.

4.3.Groundwater Quality Assessment
The suitability of groundwater for drinking and irrigation is assessed on the basis of hydrochemical analysis data.

Groundwater Quality Assessment
The suitability of groundwater for drinking and irrigation is assessed on the basis of hydrochemical analysis data.

Assessment of Groundwater Quality for Drinking Purposes
WQI is one of the most comprehensive ways to address the overall quality of groundwater [82]. The composite influence of groundwater chemical parameters on overall groundwater quality is provided by the WQI, which is calculated by considering the standards recommended for drinking purposes by the WHO [55].
WQI values are classified into five categories: excellent (<50), good (>50), poor (>100), very poor (>200) and water unsuitable for drinking (>300). Table 5 illustrated the categories of groundwater quality according to WQI while the spatial distribution of water types is presented in Figure 9.

Assessment of Groundwater Quality for Irrigation Purposes
The suitability of groundwater for irrigation is assessed through United States Salinity Laboratory (USSL) diagram (1954) and Wilcox diagram [83] along with some indices, such as SAR, RSC, %Na, PI, MH, KR and PS. A statistical summary of irrigation quality indices of groundwater samples is presented in Table 6. SAR or Alkali hazard is an important tool to determine the groundwater suitability for irrigation purposes. Osmotic activity is reduced by higher salinity which hinders water to reach the branches and leaves of the plants, leading to their inferior production [84]. According to SAR, groundwater is classified as low (SAR < 10), medium (10 < SAR ≤ 18), high (18 < SAR ≤ 26) and very high (SAR > 26) sodium hazard. In the current study, the value of SAR ranges from 0.65 to 16.21, with an average of 3.41 depicting a low or medium sodium hazard. The USSL diagram ( Figure 10) shows that 44 samples (73.78%) fall in C 2 S 1 and C 3 S 1 categories which can be used for irrigation purpose with little harm of Na + exchange. Four samples belong to C 3 S 2 category, six samples to C 4 S 2 category, four samples to C 4 S 3 category, while only one samples fall in C 4 S 4 category. Water falling under these categories cannot be recommended for any agricultural practices.  SAR or Alkali hazard is an important tool to determine the groundwater suitability for irrigation purposes. Osmotic activity is reduced by higher salinity which hinders water to reach the branches and leaves of the plants, leading to their inferior production [84]. According to SAR, groundwater is classified as low (SAR < 10), medium (10 < SAR ≤ 18), high (18 < SAR ≤ 26) and very high (SAR > 26) sodium hazard. In the current study, the value of SAR ranges from 0.65 to 16.21, with an average of 3.41 depicting a low or medium sodium hazard. The USSL diagram ( Figure 10) shows that 44 samples RSC is an important index for the evaluation of groundwater suitability for irrigation. It can be estimated by subtracting alkaline earth metals (Ca 2+ + Mg 2+ ) from carbonates and bicarbonates (CO 3 2− + HCO 3 − ). Adsorption of sodium in soil is attributed to the high value of RSC [85]. Groundwater is considered unsuitable if RSC value exceeds 2.5. According to RSC, 98.30% samples of the present study have been found to be suitable for irrigation purposes. Irrigation water with high sodium percentage reduces the permeability of the soil, which consequently affects the plant growth, thus making it an important index for the evaluation of groundwater on agricultural scale [86]. Groundwater having less than 60% Na is considered suitable for irrigation use. %Na value ranges from 15.64 to 86.32 having a mean value of 41.70. 91.52% samples fall in excellent to permissible limits. According to Wilcox diagram (Figure 11  The influence of ion contents in groundwater on the permeability of the soil is evaluated by Permeability Index (PI) proposed by Doneen [87]. Based on PI, values less than 25 are considered unsuitable for irrigation. In the current study, all samples have been found suitable for irrigation on PI basis.
Another tool for assessing the agricultural suitability of groundwater is MH, proposed by Szabolcs and Darab [88]. Sodication in the soils increases with the subsequent increment of Mg 2+ content relative to Ca 2+ , which consequently results in the dispersion of clay particles hence damaging the soil structure by decreasing the hydraulic conductivity. MH value less than 50 is considered suitable for irrigation. Table 7 shows that 69.49% of samples have been found in the suitable range.
KR is another important indicator for the evaluation of groundwater for agricultural suitability proposed by Kelly [89]. A Kelly's ratio value greater than 1 indicates excess level of sodium in groundwater, while less than 1 Kelly's ratio is considered suitable for irrigation [90]. In the current study, as per KR, 42 samples (71.19%) fall in the suitable range for irrigation purposes. The influence of ion contents in groundwater on the permeability of the soil is evaluated by Permeability Index (PI) proposed by Doneen [87]. Based on PI, values less than 25 are considered unsuitable for irrigation. In the current study, all samples have been found suitable for irrigation on PI basis.
Another tool for assessing the agricultural suitability of groundwater is MH, proposed by Szabolcs and Darab [88]. Sodication in the soils increases with the subsequent increment of Mg 2+ content relative to Ca 2+ , which consequently results in the dispersion of clay particles hence damaging the soil structure by decreasing the hydraulic conductivity. MH value less than 50 is considered suitable for irrigation. Table 6 shows that 69.49% of samples have been found in the suitable range.
KR is another important indicator for the evaluation of groundwater for agricultural suitability proposed by Kelly [89]. A Kelly's ratio value greater than 1 indicates excess level of sodium in groundwater, while less than 1 Kelly's ratio is considered suitable for irrigation [90]. In the current study, as per KR, 42 samples (71.19%) fall in the suitable range for irrigation purposes.
The agricultural suitability of groundwater is also assessed by PS which is defined as the chloride concentration plus half of the sulfate concentration. Doneen [91] proposed that agricultural suitability is not dependent on the concentration of soluble salts. Every successive irrigation helps in the precipitation and accumulation of low soluble salts, whereas the salinity of the soil is enhanced by the concentration of highly soluble salts. Groundwater is considered suitable, when PS values are less than 10. For the present study, PS values show that 43 samples (72.89%) are suitable for irrigation purposes.

Conclusions
In order to carry out the current study, an amalgamation of statistical analyses, graphical techniques and hydrochemical modeling were used for comprehensive understanding of the groundwater chemistry, its evolution and suitability for drinking and agricultural purposes in the delimited area of research.
Statistical analyses demonstrate that the abundance of cations is in the order: Na + > Ca 2+ > Mg 2+ > K + , while the abundance of anions is in the order: HCO 3 − > Cl − > SO 4 2− . The abundance of Na + and HCO 3 − proves that silicate weathering is the eminent phenomenon controlling the major ion chemistry of the groundwater in the research area. This is also supported by the correlation analysis and graphical relationships between ions that reveal that ion exchange and rock weathering-like the dissolution of halite, albite, and dissolution of carbonate minerals-are important rock-water interactions, which govern the evolution of groundwater chemistry. Furthermore, rock dominance has been found as the key natural factor governing the groundwater evolution as depicted by the Gibbs diagrams, while few samples falling in the evaporation dominance propose the influence of evaporation in shallow groundwater depth zone. Hydrochemical facies are predominantly of mixed CaMgCl and Na-Cl type with few samples of Ca-HCO 3 type, constituting fresh recharged water. Saturation indices computed by geochemical modelling indicate that the aqueous phase is under-saturated with respect to evaporites like halite and gypsum (negative values), while there is equilibrium to the over-saturated phase with respect to carbonates like calcite and dolomite (positive values). Computed values of WQI shows that 71.18% samples are safe for drinking purpose while 28.82% fall in unsuitable range. The contributing factors towards the aforementioned range of groundwater samples include dissolution process and effective leaching of rock salt and gypsum-bearing rock formations. The majority of samples have been found suitable for irrigation purposes as per the USSL diagram, Wilcox diagram and other agricultural indices.