Upper-Doab is a section of Ganga-Yamuna Doab lying in the state of Uttar Pradesh, India with latitudinal extent between 29.97° N and 28.4° N, and longitudinal extent between 77.08° E and 78.09° E. The region includes the districts of Saharanpur, Muzaffarnagar, Meerut, Baghpat, Ghaziabad, Gautam Buddha Nagar, and Bulandshahr (Figure 1), and covers about 18,550 sq. km of area, which is about 7.7% of the total area of Uttar Pradesh, and about 30.7% of the total area of Ganga-Yamuna Doab. Administratively, the region is bounded by Uttarakhand in the north, Haryana and Delhi in the west, and districts of Uttar Pradesh in the south and east. Forming part of the Indo-Gangetic plain, this is one of the most fertile regions in India. Major cities are Meerut, Saharanpur, Ghaziabad, and NOIDA. The region produces sugarcane, fruits, vegetables, pulses, and wheat on a massive scale, and manufactures automobile radiators, insulated wires, brass and copper utensils, refined sugar, textile machinery, etc. The region has a sub-humid and tropical climate with summer commencing in April and ending by late June with the onset of monsoon. The summer is hot and dry with a maximum daily temperature between 38°C to 43°C. January is the coldest month of the year with the lowest temperature around 2°C. The precipitation in the region ranges from 650 mm per year in Baghpat to 912 mm per year in Saharanpur district. Of which, about 85% of annual precipitation occurs during monsoons (CGWB, 2022). As the region is under high pressure owing to the urban growth and eastward extension of population and industrial set up around national capital territory of Delhi (Figure 1), massive groundwater mining to meet domestic, agricultural and industrial needs have the possibility of adversely impacting the quality of groundwater in the region.

Indo-Gangetic plain formed about 15 million years ago in response to upliftment of the Himalayan Plateau with lithospheric loading and depression of the Indian continental plate, remains the world’s largest area of modern alluvial sedimentation (Bonsor et al., 2017). Geologically, it has been formed by the sediments (mainly pebble, sand, gravel, clay, silt, and kankar) deposited by rivers flowing southward from the Himalaya over the Precambrian topography (Singh, 2004). The basin is underlain by laterally discontinuous but hydraulically interconnected semiconfined sand-rich aquifers (Prasad et al., 2015). The exploratory drilling carried out in the region identifies a three-tier aquifer system divided into confined and unconfined aquifers up to a depth of 450 m below groundwater level (mbgl). The first unconfined aquifer extends down to an average depth of 150 km. This is the most significant aquifer system as a source of water for dug wells and tube wells which are being extensively exploited for the domestic, irrigational, and industrial need of the people in the region. The second aquifer system extends between 170 mbgl to 350 mbgl, and the third aquifer system occurs below 350 mbgl, and up to 450 mbgl (Singh et al., 2014; Prasad et al., 2016; Ahmad and Khurshid, 2019). The hydrogeological studies about saline nature of groundwater in the region (Chadha, 2016) show that in the districts of Baghpat, western Meerut, central Ghaziabad, and about 75% of Bulandshahr district have saline water overlain and underlain by fresh groundwater. Whereas, Gautam Buddha Nagar district along with adjoining areas of Ghaziabad and Bulandshahr have freshwater underlain by the saline groundwater (Figure 2A). A fence diagram reporting fresh water, and brackish/saline water have also been shown in Figure 2B.

Around 70 groundwater samples from hand pump IM-II tapping phreatic aquifers have been collected from Groundwater Monitoring Stations (GWMS) established by the Central Groundwater Board (CGWB), Lucknow during the pre-monsoon period of 2021. The samples were carried in tightly sealed tarson bottles, and utmost care was taken for the samples to reach the laboratory, where the samples were analyzed as per the standard method (APHA, 2005) for bicarbonate (HCO₃), sulphate (SO₄), chloride (Cl), fluoride (F), nitrate (NO₃), total hardness (TH), calcium (Ca), magnesium (Mg), sodium (Na) and potassium (K). The potential of hydrogen (pH) and electrical conductivity (EC) was measured in situ by pH and EC meters, respectively. The titrimetric method was applied for measuring HCO₃, Ca, and Mg concentration. Whereas, a flame-photo meter was used to measure Na and K concentration. The spectrophotometric method was used to measure F, NO₃, and SO₄ concentration, and Mohr’s for Cl concentration (Nijesh et al., 2021).

Water Quality Index (WQI) is a quality rating method widely used to show the composite influence of all the water quality parameters based on the quality rating scale (Q _n ) of each parameter and their unit weight (W _n ) (Atta et al., 2022; Alsheri and Abdelrahman, 2023). Then a single score is generated to represent the water quality for domestic purposes. Weighted Arithmetic Water Quality Index (WAWQI) is one of the well-established methods to analyze water quality for domestic purposes in which Q _n is calculated using Eq. 1 and the W _n is calculated using Eq. 2 which depends upon the standard value of each parameter as prescribed by WHO (2011) (Gharibi et al., 2019; Gautam et al., 2021). The final calculation for determining the water quality is calculated using Eq. 3. Q n = C n S n × 100 (1) W n = K S n (2) W Q I = ∑ Q n W n ∑ W n (3) Where Q _n is the quality rating scale for nth water quality parameter, C_n is the observed value of nth parameter, S_n is the standard value of nth parameter, W_n is the unit weight for nth parameter, and K is the proportionality constant, calculated by K = 1 ∑ n 1 S n . The upper limit of quality standard, the proportionality constant, and the unit weight for each parameter have been mentioned in Table 1.

Groundwater suitability for irrigation has been calculated using indices such as Residual Sodium Carbonate (RSC) (Eq. 4), Sodium Adsorption Ratio (SAR) (Eq. 5), Sodium Percentage (%Na) (Eq. 6), Permeability Index (PI) (Eq. 7), Kelly Ratio (KR) (Eq. 8), Magnesium Hazard (MH) (Eq. 9), Potential Salinity (PS) (Eq. 10), Irrigation Coefficient (K_a) (Eq. 11) and Synthetic Harmful Coefficient (K) (Eq. 12). These indices are based on the comparative ionic composition of various physico-chemical parameters present in the groundwater. R S C = H C O 3 − + C O 3 2 + – C a 2 + + M g 2 + (4) S A R = N a + C a 2 + + M g 2 + / 2 (5) % N a = N a + + K + × 100 C a 2 + + M g 2 + + N a + + K + (6) P I = N a + + H C O 3 − C a 2 + + M g 2 + + N a + + K + × 100 (7) K R = N a + C a 2 + + M g 2 + (8) M H = M g 2 + C a 2 + + M g 2 + × 100 (9) P S = C l − + 1 2 S O 4 2 − (10) K a = 288 5 C l − i f   N a + < C l − 288 N a + + 4 C l − i f   C l − < N a + < C l − + 2 S O 4 2 − 288 10 N a + − 5 C l − − 9 S O 4 2 − i f   N a + > C l − + 2 S O 4 2 − (11) Where all ionic concentrations are expressed in meq/L K = 12.4 M + S A R (12) Where M represents the TDS (in g/L).

Further, the present study has used Composite Groundwater Quality Index for Irrigation (CGQII) method to have a single score to decide groundwater suitability for irrigation (Gautam et al., 2021). CGQII for each groundwater sample has been calculated using the following formulas: Q n = C n S n × 100 W h e n   t h e   w a t e r   q u a l i t y   d e c r e a s e s w i t h   i n c r e a s e   i n   i n d e x   v a l u e (13) Q n = C n S n − 1 × 100 W h e n   t h e   w a t e r   q u a l i t y   d e c r e a s e s w i t h   d e c r e a s e   i n   i n d e x   v a l u e (14) W n = K S n (15) C G Q I I = ∑ Q n W n ∑ W n (16) Where, Q_n is the quality rating scale for nth irrigation index, C_n is the observed value of nth irrigation index. S_n is the standard value of nth irrigation index, W_n is the unit weight for nth irrigation index, and K is the proportionality constant, calculated as similar to WAWQI. The standard limit, the proportionality constant, and the unit weight for each irrigation index have been mentioned in Table 2.

The analytical results of groundwater samples of the Upper-Doab region of Uttar Pradesh have been presented in Table 3. The largest variation has been recorded in EC, TH, HCO₃, Na, and Cl concentrations among all the Physico-chemical parameters in groundwater samples of the region. Overall, the ionic dominance in the groundwater samples is in the order of HCO₃ > Cl > SO₄ > NO₃ > F and Na > Mg > Ca > K. However, this sequence of dominance is not uniform in all the samples. A few samples have higher chloride concentrations than bicarbonate, and a few samples have higher nitrate than sulphate.

Based upon the chemical concentration in the groundwater samples, the chemical history of groundwater samples was determined using a piper-trilinear diagram (Figure 3). It shows that most of the groundwater samples lie in the 1^st and 3^rd quadrants of the diamond plot. This shows that Ca-Mg-HCO₃ and Ca-Na-HCO₃ types of groundwater are mostly found in this region. Similar kinds of groundwater facies have also been reported by Nijesh et al. (2021) while assessing the hydrochemical characteristics of groundwater under similar hydrogeological conditions in the Upper Ganga plain of Uttar Pradesh, India. Apart from these, Na-HCO₃ types of groundwater have also been reported, mainly in the Baghpat and Gautam Buddha Nagar districts of the region. The same groundwater facies has also been reported in the groundwater around the Hindon river basin, which drains in the south-western parts of the study area forming a major part of the alluvial plains of Gautam Buddha Nagar district (Ahamad and Khurshid, 2019). The reason for Na-HCO₃ types of groundwater is both anthropogenic and geological. On one hand, the massive extraction of groundwater to meet agricultural and domestic needs of urban population has led to lowering of groundwater table to around 45 mbgl (CGWB, 2022); and on the other, loose quaternary deposits of sand, silt, gravel and pebbles provide a suitable condition for infiltration and penetration of rainwater, irrigation flows and urban discharge. A part of this infiltrated water penetrates into the basement rocks of the discharge zone and interacts with aluminosilicates rocks present there, resulting in the formation of Na-HCO₃ types of groundwater (Borzenko et al., 2019).

Gibb’s plot best illustrates the functional sources attributing chemical constituents to the groundwater. The analysis reveals that rock-water interaction was dominantly controlling the ionic composition of the groundwater in the unconfined aquifer environment. However, at a few places in shallow aquifers, the evaporation effect was also dominant (Figures 4A, B). Further, the bivariate plot of (SO₄ + HCO₃) vs. (Ca + Mg) has been used to understand the mechanism of ion exchange between the groundwater and its host unconfined aquifer environment. The results reveal that most of the samples lie along the 1:1 line (Figure 5). This suggests that the weathering of calcite and dolomite minerals present in the aquifer environment of the alluvial plain has largely attributed chemical character to the groundwater of the region (Gautam et al., 2022; Yao et al., 2022). However, in about 10% of the groundwater samples of Meerut, Ghaziabad, and Gautam Buddha Nagar districts, the process of ion exchange has been found dominant due to excess sulphate or bicarbonate. This suggests the process of silicate weathering in the clayey aquifer environment of the region. Apart from this natural cause, there is a greater chance of ion-exchange between calcium and magnesium from carbonate minerals and sodium from groundwater of the urban areas, as Ghaziabad and Gautam Buddha Nagar are the highly urbanized and industrialized districts of the region being located near-to and towards groundwater flow direction of National capital of Delhi.

The intake of various ions is crucial for the proper functioning of body metabolism. However, human health is very sensitive to the intake of the amount of ionic concentration. Even the small presence of trace elements and other organic pollutants can be potentially severe to human health. Highly acidic water can cause digestive problems for humans by reducing insulin sensitivity in case of lower pH and inducing whole-body acid-base imbalance (Hansen et al., 2018). Results reveal that the pH of groundwater ranges between 7.6 and 8.7 (Table 3), which is acceptable for domestic use. High salinity (measured by EC) above 1,000 µS/cm has been recorded in the groundwater samples of Baghpat, Chaprauli, Binauli, Pilana, Khekra, Sikandrabad, Shikarpur, Jewar, Loni, Razapur, Bhojpur, Meerut, Sardhana, Burdhana, Charthawali and Nakur, which invites greater human concern, as high salinity in water affects blood circulation in humans (BIS, 2012). Calcium greater than permissible limit of 75 mg/L were reported in the groundwaters of Loni, Hastinapur, Sardhana, Charthawal, Nakur and Sadauli Qudim, where continuous intake of highly concentrated calcium water may cause digestive disorder, dehydration, diarrhoea etc. (Bhuiyan and Ray, 2017). Higher magnesium concentration (>50 mg/L) were reported at only two places i.e., Sardhana and Sarsawa, where people might be infected with kidney dysfunction and acute renal failure (Swaminathan, 1998). Higher intake of sodium in drinking water may be associated with hypertension and chronic kidney disease (Fadeeva, 1971; BIS, 2012; Bhuiyan and Ray, 2017). The study found that groundwaters at a few places in Gautam Buddha Nagar and Bulandshahr districts have reported higher sodium concentration, where people are susceptible to these diseases associated with higher intake of sodium ion. To assess the suitability of groundwater for domestic consumption, sometimes the spatial distribution of individual ions is considered. However, it has been found arbitrary that a groundwater sample is found suitable for domestic use considering calcium, and unsuitable when considering sodium ion concentration. Therefore, to have a single score for assessing the quality of water, WAWQI has been widely used in the research domain that considers the proportionate value of all the ions considered for assessing water quality (Adimalla and Qian, 2019; Ren et al., 2022). Results reveal that about 10% of the groundwater in the region was found poor to unsuitable for domestic use (Table 4). This includes areas of Gautam Buddha Nagar, Baghpat, and Muzaffarnagar districts (Figure 6).

This is largely due to the higher concentration of nitrate and potassium in Baraut (Baghpat), and Khandhal, Shamli (Muzaffarnagar), and sodium and fluoride in Dankaur (Gautam Buddha Nagar). The source of higher concentrations of these minerals are natural (fluorite minerals, silicate minerals, and evaporite deposits), and anthropogenic (excessive groundwater extraction, untreated waste discharge and excessive fertilizers in agriculture) both.

Groundwater could be analyzed for domestic consumption considering individual ions or all ions as in WAWQI; but for evaluating groundwater suitability for irrigation purposes, the relative concentration of one ion over the other is the most significant. Therefore, about nine indices have been used in various studies analyzing the groundwater status for irrigation purposes. The present study also analyses the groundwater suitability for irrigation using all these indices one by one, each having a specific significance.

RSC calculates the excess of CO₂ and HCO₃ over Ca and Mg combined. This tends to the precipitation of calcium and magnesium. The very high value of RSC gives rise to the possibility of sodium ion adsorption, especially in clayey soil having a high capacity for cation exchange (Singh et al., 2008). This may further lead to the deposition of sodium carbonate making the soil alkaline and reducing soil productivity (Das and Nag, 2015). Results reveal that only about 33% of the region has good quality groundwater concerning RSC, and about 39% of the groundwater has been found unsuitable for the use of irrigation purposes (Table 5). The areas included in the unsuitable category are southwestern parts including Gautam Buddha Nagar, Ghaziabad, Baghpat, Meerut, and Bulandshahr districts (Figure 7A). SAR considers excess sodium ion over calcium and magnesium combined. Its higher concentration affects the growth of seedlings and crop productivity (Nagaraju et al., 2016). About 98% of the groundwater samples were under the excellent category, which is a good sign for higher crop productivity (Table 5). However, it was found higher in the southern parts of Gautam Buddha Nagar district (Figure 7B). Sodium Percentage is another index to measure sodium hazard in groundwater. Results reveal that about 21% of the region in the south-western parts has higher sodium concentration in comparison to the total cations present in the groundwater, making it unsuitable for use (Table 5; Figure 7C). This may alter soil structure, and reduce soil permeability and aeration (Bouderbala, 2017). Sodium value more than calcium and magnesium combined also makes groundwater unsuitable for irrigation as calculated by KR. As per this index, about 41% of the area in south-western parts has groundwater unsuitable for irrigation (Table 5; Figure 7D). Groundwater with a high concentration of calcium, magnesium, sodium, and bicarbonate should not be used for irrigation for a longer period (Gautam et al., 2021). A groundwater sample having a PI value of 75% or above the maximum permissible limit is considered suitable for the use of irrigation (Class I and II); whereas, below 25% of maximum permeability makes it unsuitable for the use of irrigation (Class III) (Doneen, 1964). Results reveal that 46 groundwater samples out of 71 have been found unsuitable for irrigation use. Further, for groundwater use in irrigation, calcium, and magnesium must be in equilibrium with each other for good crop yield. Fortunately, this equilibrium has been maintained in most of the groundwater samples in the region (Table 5; Figure 7E). Otherwise, this would have resulted into hardness of the soil, reducing soil productivity (Nagaraju et al., 2016). Further analysis reveals that the groundwater of about 99%–100% of the region has been found suitable for irrigation use concerning potential salinity, synthetic harmful coefficient, and irrigation coefficient (Table 5; Figures 7F–H).

It can be noted from the discussion above that, many groundwater samples were found suitable concerning one index and found unsuitable concerning the other. Therefore, CGQII has been used to get a single score for a sample for considering its suitability for irrigation. Results reveal that groundwater of about 25% of the region including Gautam Buddha Nagar, Bulandshahr, Ghaziabad, Meerut, and Baghpat has been found unsuitable for irrigation purposes (Table 6; Figure 8). It must be noted that being nearer to National Capital of Delhi, the western region (most of Upper-Doab region) has greater levels of urbanization with Ghaziabad and Gautam Buddha Nagar district, having more than 50% of their population residing in urban areas (Raj and Singh, 2017). The region has experienced immense growth in industrial sectors after economic liberalization in 1991. Western Uttar Pradesh has a greater number of sugar mills in the districts of Muzaffarnagar, Baghpat, Meerut, and Saharanpur. Apart from this, textile industries, wooden and furniture industries, paper industries, glass industries, and brass and cement industries are also located in this region. These activities largely contribute to making the groundwater unsuitable for irrigation in the region. Similar kind of results has also been obtained in analyzing the groundwater quality in the Ghaziabad district in a separate study carried out by Chabukdhara et al. (2017). The impact of land use on the overall quality of groundwater in the Ghaziabad district of Uttar Pradesh shows that the quality of groundwater is deteriorating at an alarming rate due to improper management of land use activities (Tyagi and Sharma, 2018).

It must also be noted that the region is further experiencing many fold increase in the highway and expressway sectors with the construction of the Delhi-Meerut Expressway, under construction Delhi-Meerut Regional Rapid Transit System (RRTS) and the green-field expressway of Delhi-Dehradun traversing the whole Upper-Doab region from south to north. This would lead to a greater concentration of population and infrastructural development for industrial purposes resulting in undue pressure on the existing groundwater resources in the region concerning groundwater quality and quantity. The adverse impact of highly urbanizing areas on groundwater quality has also been reported in the developing region of the world at many places under similar geological conditions (He et al., 2009; Lu et al., 2018).