Hydrogeochemical characterization of groundwater in mountainous catchment and its suitability for drinking purposes in Irob, Tigray, Northern Ethiopia

Ethiopia's semi-arid mountainous region is primarily dependent on groundwater for its drinking water supply. The semi-arid regions often face water stress due to erratic and unreliable rainfall (Meaza et al. 2018). There is no doubt that there is a growing global need for groundwater for industrial, agricultural and residential uses. In addition to increasing groundwater exploitation, climate change and human activities also pose significant risks to groundwater quantity and quality. Groundwater is considered safer and cleaner for drinking than other water supply sources. According to the United Nations World Water Development Report (UNWWDR 2022), about one-fourth of the world's population uses groundwater for drinking purposes. However, natural and anthropogenic processes could degrade the quality of groundwater (Yetiş̧ et al. 2019; Liu et al. 2020; Sharma et al. 2022). Hence, before water is labeled as potable, it has to conform to certain water quality standards. Knowledge of hydrogeochemical characteristics of groundwater is crucial for assessing its quality and suitability for various applications. In this context, numerous studies have shown how both natural and man-made elements influence groundwater chemistry (e.g. Abanyie et al. 2020; Ahmad et al. 2020; Alemayehu et al. 2020; Kumar et al. 2021).

Knowledge of the hydrogeochemical processes is particularly crucial for groundwater quality given that the chemical characteristics vary along the flow systems. Hydrogeochemical evolution influences the quality of groundwater characteristics through geogenic processes. The hydrogeochemical process of the mountainous catchment is influenced by the composition of recharge waters and the interaction with the aquifer materials (Somers & McKenzie 2020). Mountain watersheds are characterized by a complex hydrogeochemical evolution, despite being widely recognized as an important water supply. Therefore, it is crucial to explore groundwater characteristics to provide adequate quantity and quality for downstream populations.

According to Appelo & Postma (2004), the composition of recharge water, water–rock–soil interaction in the unsaturated zone, residence time and geochemical and biochemical reactions occurring within the aquifer are some of the factors that affect the quality of groundwater in addition to physical, chemical and biological components. Geogenic processes (rock weathering, mineral dissolution, ion exchange and evaporation) and anthropogenic sources (irrigation-return flows, wastewaters, agrochemicals and building activities) are the primary factors influencing the chemical composition of groundwater (Subba et al. 2017; Sako et al. 2018; Lermi & Ertan 2019; Alemayehu et al. 2020).

Nitrates can enter groundwater through chemical fertilizers used in agricultural land (Tchobanoglous et al. 2023). Excessive nitrate concentrations in drinking water pose an immediate and serious health risk to infants (19). The nitrate ions react with blood hemoglobin, thereby reducing the blood's ability to store oxygen, resulting in a disease called Blue Baby (APHA 2017). A moderate amount of fluoride (F⁻) in drinking water contributes to good dental health (APHA 2017). About 1.0 mg/L is effective in preventing tooth decay, especially in children (APHA 2017). However, excessive amounts of fluoride lead to discolored teeth, a condition known as dental fluorosis (Davis & David 2008; Davis 2010). Furthermore, the sodium content in table salt has been linked to kidney and heart disease (WHO 2017).

The groundwater chemical composition represents the water–rock interaction along the flow pathway. Several studies (e.g. Alemayehu et al. 2011; Ekanem et al. 2020) noticed a knowledge gap regarding the natural process that influences water quality in the aquifer system in the region. The increased total ion concentration indicates the groundwater flow path along which it interacts. Understanding the hydrogeochemical process and major ions helps to investigate the compositional variations in groundwater and the source of the ions. Human activities, ion exchange and the chemical weathering of the country rocks, which was linked to the dissolution of minerals and carbonates (Ayadi et al. 2018; Burhan et al. 2023), mostly impacted the groundwater quality in Northwestern Tunisia.

Numerous graphical techniques and interpretations of numerous indicators can be used to assess the quality of groundwater and determine the distinct processes of hydrogeochemistry characteristics that influence groundwater chemistry (Van Green et al. 2019; Kumar & Singh 2020; Mallick et al. 2021; Dashora et al. 2022; Khattak et al. 2022). Researchers point out that groundwater characterization is a powerful tool for addressing a variety of geochemical issues. So a better understanding of the hydrogeochemical mechanisms that regulate groundwater chemistry could aid in its efficient management and long-term development.

Groundwater can be used for industrial and agricultural applications if the quality is appropriate for drinking (Subba et al. 2017). Therefore, assessing the contamination and quality of groundwater is crucial to applying remediation and water resource management techniques. In Ethiopia, the majority of drinking water sources have relatively low electrical conductivity at the national level; however, in the Tigray region, 22% of water sources have high electrical conductivity concentrations (Kassegne et al. 2020). Gebrewahd et al. (2020) conducted a related study in northern Ethiopia Tigray region and found that approximately 34% of the drinking water in this region had a high hygiene risk value, and Klebsiella species were a common pathogen in the study area (Bekuretsion et al. 2018).

The Assabol dam in the Irob region stores a part of the flood runoff water during the rainy season, and the local people use the water for irrigation and drinking water supply (Andress 2007). The dam water can be classified into the ‘hard’ category because the total hardness value of the water samples was above WHO permissible limits for drinking purposes and is not suitable for drinking purposes without appropriate treatment (Shifare & Seyoum 2015). According to Shifare & Seyoum (2015), some of the physical and chemical properties of the dam water (total hardness, ammonium and alkalinity), bacteriological quality parameters (total coliform) and heavy metals (lead (Pb) concentration) exceeded the maximum permissible limit of WHO standard for drinking water.

The present investigation area is located in the semi-arid climate zone of the eastern part of the Tigray region, a complex mountainous hydrogeologic system with limited data. In the region, the groundwater quality issue has become more serious than the quantity problem, as environmental threats are increasing from time to time. In addition, the rising need for clean drinking water poses major challenges for the region. The water supply mainly groundwater through hand-dug wells to the Irob area's is affected due to the dispute between Eretria and Ethiopia. Many organizations have drilled numerous boreholes to support the affected people. While many boreholes yield good groundwater quality, few of them were also banned from immediate use because of complaints about the quality from the community. Policy makers can benefit from the helpful information provided by the classification and source identification of dissolved ions in groundwater, which can help ensure the sustainable management of these essential resources.

Little attention has been paid to the assessment of groundwater quality and no attempts have been made to study groundwater quality, despite the public concern in the study area. A previous study (Hayelom & Gebregzabher 2015) determined the content of some trace elements in Dowhan town. Consequently, the paper provides a comprehensive groundwater quality assessment and compares it against the WHO standards. Therefore, the current study aims on assessing the groundwater quality and characterize the primary hydrogeochemical processes that control the groundwater quality and chemistry of the Irob catchment in Tigray northern Ethiopia using an integrated approach of field observations, and analytical and graphical analyses.

Metavolcanic rocks of the area are described by the intercalations of metarhyloties; metaaglomerates, tufaceous slate and metabasalts. Signs of alteration developments such as epidotization and kaolinization have been observed and show gradual contact with metasediments.

The metavolcanic clast consists of welded tuff, metabreccia and metaagglomerate rocks and the size, shape and chemical composition of the clasts vary considerably. The composition of the clasts is between felsic and mafic, and this rock type is characterized by the formation of a steep topography.

Metasedimentary rocks are characterized by dolomite rocks inter-beaded with meta-limestone, phyllite and slate. Phyllite and slate rocks exhibit highly developed foliation and exhibit a variety of colors, including brown, light gray and dark gray. In this rock type, the occurrence of altered pyrite crystals with cubic structures is observed. The mountainous areas consist of a series of ridges composed of K-feldspar rich granite intrusions. The granitic dikes/sills have intruded the bedrocks. Granite has developed high peak ridges oriented in an east–west direction and has an area of almost 3 km². Along the contact surface of the host rock (metavolcanic rock) in the northeast direction, the granitoid body has developed white, powdery changes due to kaolinization. In the current study area, a normal fault is observed cutting the granite into two segments.

The quaternary sediments cover a small area and can be seen on both sides of riverbanks and in the flood plains. Weathering and subsequent erosion of the surrounding rock play a significant role in the formation of these deposits.

The hydrogeological system of the study area is influenced by geology, geomorphology and tectonic activities. The occurrence of groundwater is expected in the weathered shallow metavolcanic, metasedimentary and alluvial aquifers. In shallow groundwater systems, the porosity network is favorable for the accumulation and movement of water. Flow and storage in the aquifer system likely depend on the thickness of the alluvial and contained fracture systems. The reduction in permeability that occurs in deep aquifers is due to fill minerals that subsequently reduce yield. A lack of groundwater connectivity and heterogeneity could explain the lateral variation in aquifer chemistry and yield. Geological descriptions and well records are very important in determining aquifer properties. In general, metamorphic rocks are low-productivity aquifers characterized by complex aquifer systems (Briški et al. 2020; Chidichimo et al. 2023). The groundwater recharge zones are the highlands of the Irob Mountains. The wells drilled in the metavolcanic and metasedimentary rocks of the study area measured yields of 0.091 and 0.98 l/s, respectively.

Fifteen groundwater samples (13 borehole water, 2 spring water) were collected during the dry season of March 2020 with a borehole depth of 5–60 m. To make it easier to find the right sample, a sampling measure was set up before data sorting. Both inactive and functional hand pumps for human use were selected for sample collection. Different geological units, land use characteristics, geomorphology, flow direction and accessibility were the attributes used to collect representative groundwater samples (Figure 1).

To ensure the quality of the data, the standard protocol prescribed by APHA (2017) was adopted for sampling, preservation, transportation and analysis. The water was pumped long enough to clean the well before sampling. The double-caped 1,000 ml high-density polyethylene (HDPE) storage bottles were properly cleaned with dilute HNO₃ acid followed by distilled water and finally, sample containers were washed three times with the sample solution. All samples were filtered with 0.45 μm syringe filters and then HNO₃ solution was used to preserve samples for cation analysis. However, the samples used for anion analysis were not acidified. Following the collection of groundwater samples, the HDPE bottles were packed in a cool box, labeled appropriately for identification and taken to the laboratory for analysis. The in situ measurements of temperature, pH and electrical conductivity (EC) were carried out using a portable pH meter model HANNA HI9913. To prevent cross-contamination between samples after measurement, the probe used for in situ pH, EC and temperature measurements was rinsed with deionized water. Total dissolved solids (TDS) were calculated from EC using a cation factor of 0.64 (Brown et al. 1970). Using methyl orange as a pH indicator, total alkalinity was also measured on site using HCl acid titration.

The water sample analysis was carried out in the geochemistry laboratory Mekelle University. A laboratory method according to APHA (2017) guidelines was used to determine major ions. Atomic Absorption Spectrometer 5Ob Variant was used to analyze the major cations such as Na⁺, K⁺, Ca²⁺ and Mg²⁺. While ultraviolet/visible (UV/Vis) Spectrophotometer Lambda EZ 201(Double Beam) was used to determine ions like Cl⁻, ⁠, ⁠, ⁠, F⁻, and by keeping the reaction periods and analytical reagents as per the manufacturer instruction manual.

The total hardness of the water samples was determined by Ethylenediaminetetraacetic Acid (EDTA) and concentration of Ca and Mg. Bicarbonate and alkalinity were determined by titration method with an indicator of methyl orange and titrant 0.1 N HCl (APHA 2017).

Instruments used for all analyses were pre-calibrated with standard solutions or according to company guidelines to ensure accuracy and precision for quality assurance and control (QA/CQ). All electrodes were thoroughly cleaned with deionized water before each measurement, both in the laboratory and in the field. Prior to each use, the probes were conditioned in the sample to ensure the ideal stabilization time. To avoid cross-contamination, samples were handled using sterile latex gloves and laboratory coats. Analytical blanks and standard references were also used.

To develop spatial maps for physicochemical parameters, interpolation based on inverse distance weighted (IDW) parameters was applied. In the IDW approach, the unidentified values are calculated based on the nearby points rather than the distant points.

The assessment of hydrogeochemical mechanisms and the origin of chemical components in groundwater was calculated using ionic molar ratios and graphical plots. Piper and Schoeller diagrams were plotted using Aquachem version 4.1 software package. This Aquachem software program is also used to identify the hydrochemical facies/water types of the groundwater samples based on major ions.

Descriptive statistical chemical analysis of groundwater samples was done using SPSS software package version 20. Diagrams such as Gibbs diagrams and scatter diagrams between different major ions were used to identify the source water chemistry.

Table 1 presents the laboratory results of physiochemical properties of groundwater samples collected and analyzed in 2020.

Table 1

Descriptive statistics for the chemical analysis of groundwater samples (N = 15) and classification of groundwater quality based on suitability for drinking purposes

Parameter .	Min. .	Max. .	Mean .	SD .	WHO (2017) acceptable limit .	% Samples above standard .
pH	7.36	7.89	7.62	0.13	6.5–8.5	0
EC	718	2,410	1,452	543.98	1,500	46.67
TDS	512	1,719	1,045	388.25	1,000	46.67
TH	258	1,292	647	322.89	500	60
TA	135	360	266	71.44	200	80
Ca2+	80	330	196	91.20	200	60
Mg2+	14	114	37.7	33.16	150	0
Na+	19.1	51	34.3	9.98	200	0
K+	2.04	34.07	7.96	8.52	30	6.67
	165	433.1	307	87.38	300	60
	98.6	565	284	180.81	250	53.33
Cl−	26	42.5	35.5	5.92	250	0
	15.2	37.21	20.5	5.92	50	0
	0.02	0.18	0.07	0.05	3	0
F−	0.16	1.31	0.52	0.33	1.5	0

Parameter .	Min. .	Max. .	Mean .	SD .	WHO (2017) acceptable limit .	% Samples above standard .
pH	7.36	7.89	7.62	0.13	6.5–8.5	0
EC	718	2,410	1,452	543.98	1,500	46.67
TDS	512	1,719	1,045	388.25	1,000	46.67
TH	258	1,292	647	322.89	500	60
TA	135	360	266	71.44	200	80
Ca2+	80	330	196	91.20	200	60
Mg2+	14	114	37.7	33.16	150	0
Na+	19.1	51	34.3	9.98	200	0
K+	2.04	34.07	7.96	8.52	30	6.67
	165	433.1	307	87.38	300	60
	98.6	565	284	180.81	250	53.33
Cl−	26	42.5	35.5	5.92	250	0
	15.2	37.21	20.5	5.92	50	0
	0.02	0.18	0.07	0.05	3	0
F−	0.16	1.31	0.52	0.33	1.5	0

All values are in mg/L except pH, EC, μs/cm at 25 °C.

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The majority of groundwater alkalinity comes from carbonates and bicarbonates (Reda 2016; Asmamaw & Debie 2023). The alkalinity concentration is between 135 and 360 mg/l (Table 1). 80% of water samples measured for alkalinity were above the WHO (2017) acceptable levels. Water with a hardness above the permissible limit may lead to lime scale deposits in the treatment plants, the distribution system and in the pipes and tanks within buildings, depending on how other factors such as pH and alkalinity interact (WHO 2017). Alkalinity was measured higher in the southern and northern parts of the area, where meta-dolomite and meta-limestone aquifers are predominant (Figure 3(b)).

The EC value of the water samples ranges from 718 to 2,410 μS/cm with an average value of 1,452 μS/cm. 46.67% of the water samples show concentrations above the desirable limit set by WHO (2017) (Table 1). This shows that the groundwater from which these samples were taken is unsuitable for drinking. The high EC value could be related to lithologic components and anthropogenic practices in the area. The wide EC range observed is a sign of the presence of dissolved salts such as potassium and sodium chlorides. Salinity and electrical conductivity are connected. High salinity levels cause cholera and other waterborne diseases like diarrhea (Grant et al. 2015).

The total hardness in the area varies between 258 and 1,292 mg/l with an average value of 647 mg/l (Table 1). 60% of the water samples have total hardness above the WHO acceptable limit (Table 1). Consumption of water with a total hardness above the permissible limit can have a laxative effect (Davis & David 2008), and high total hardness values may promote the formation of kidney stones and the deposition of white scales on the piping systems (Krishnan et al. 2005). Higher hardness values and alkalinity were also measured in the southeastern and northern parts of the study area. The dissolution of the carbonate minerals of the dolomite and meta-limestone aquifers is responsible for the higher total hardness (Figure 3(c)).

The TDS values of groundwater in the studied area vary between 512 and 1,719 mg/l with an average value of 1,045 mg/l and 46.6% of the water samples are above the WHO acceptable limit (Table 1). The spatial variation map of TDS shows that more significant TDS values are recorded in the northern, central and southwestern parts (Figure 3(d)). Gradual increases in TDS values were considered to be the result of water–rock interaction processes throughout the flow path. However, some groundwater samples in recharge areas have higher TDS values. This is because groundwater flow in such areas is restricted by secondary fill clay layers, sills and dykes, which increase the residence time to react with the rock.

Calcium and magnesium are found in varying amounts of groundwater, which comes from the surrounding rocks. The most abundant cation in the area is calcium. Its concentration varies from 80 to 330 mg/l and its mean value of 196 mg/l (Table 1) and 60% of the water samples show a calcium concentration above the WHO acceptable limit (Table 1). High levels of calcium can lead to scaling (El Baba et al. 2020). Moreover, the concentrations of magnesium vary from 14 to 114 mg/l with a mean value of 37.7 mg/l (Table 1). The concentration between water sources varies greatly.

The Na⁺ concentration varies from 19.1 to 51 mg/l with a mean of 34.3 mg/l and all samples are within the WHO permissible limit for sodium. The spatial variation map of Na⁺ (Figure 4(c)) shows a relatively higher value in the western and northern regions of the research area; where the predominantly metavolcanic rock occurs. The lower concentration of Na⁺ shown in the eastern part of the study area could be due to the ion exchange process with calcium (Su et al. 2023).

The potassium concentration varies from 2.04 to 34.07 mg/l with a mean concentration value of 7.96 mg/l (Table 1). The measured concentration in the groundwater samples varies greatly. The spatial variation map of K⁺ shows a relatively higher value in the southwest and northeast parts of the study area, where metavolcanic and granitic rocks predominate (Figure 4(d)). In contrast to the Na⁺ concentration, K⁺ is immobile and, due to the higher resistance of weathering rocks containing K⁺ minerals, rarely occurs in low concentrations in groundwater could lead to fixation in the form of clay minerals (Kolahchi & Jalali 2007; Berhe et al. 2021).

The most dominant anion in the study area is and its concentration varies between 165 and 433.1 mg/l. The second most abundant anion is and its concentration ranges from 98.6 to 563 mg/l with a mean concentration value of 284 mg/l. 60% of the water samples measured for bicarbonate and 53.33% of the water samples measured for sulfate concentration were above the WHO (2017) permissible limit (Table 1).

Calcium and magnesium salts, bicarbonates and sulfates are the main causes of water hardness (Sengupta 2013) and consuming hard water may lead to dry skin and hair (Ronald 2019). Using hard water can change the pH of the skin, reducing the skin's ability to protect against bacteria and infections. Several studies reported that sore throats and kidney problems were observed due to regular consumption of hard water over a very long period of time (Ronald 2019).

F⁻ shows a similar trend to Cl⁻ at almost all sites, revealing that the low concentration comes from a non-geogenic source (Figure 5(c) and 5(d)).

The measured concentration of and in the study area varies from 15.2 to 37.2 mg/l, and from 0.02 to 0.18 mg/l, respectively. All of these ions are within the WHO desirable limit water for drinking purposes. Forms of nitrogen such as nitrate and nitrite most commonly cause groundwater pollution (Böhlke et al. 2006; Zhao et al. 2023). The use of agricultural fertilizers and the discharge of animal and human wastes are considered to be the most common sources of nitrate concentrations (Welch et al. 2000; Ediagbonya et al. 2015; Craswell 2021; Zhang et al. 2021). As shown in the maps (Figure 6(a) and 6(b)), and concentrations are measured slightly higher in the central parts of the present research area near the towns and agricultural areas. This slight variation is a result of domestic sewage, detergents and using agrochemicals during agricultural activities.

The flow of groundwater in the mountainous area has a high velocity and a short residence time during circulation; as a result, the groundwater is not able to enter into significant water–rock interactions. The groundwater in the mountainous areas is fresh with TDS <1,000 mg/l and the water type is mainly Ca–HCO₃–SO₄ and Ca–Mg–HCO₃–SO₄ (Table 2). The hydrochemical study generally shows that the geochemical composition of groundwater in the area is spatially variable due to the geological differences caused by hydrochemical evolution. The geochemical composition of the groundwater suggests the hydrochemical evolution from slightly mineralized Ca–Mg–HCO₃–SO_4, Ca–HCO₃–SO₄ to moderately mineralized Ca–Mg–SO₄–HCO_3, Ca–SO₄–HCO₃ and Ca–Na–HCO₃–SO_4, close the flow direction of groundwater. As the water moves from high-elevation areas (recharge) to lower-elevation (discharge) areas, the geochemical characteristics appear to change.

Scatter diagrams of various ionic elements have been applied to understand the different hydrogeochemical processes that actively contribute to the evolution of water chemistry (Berhe et al. 2021), and the characterization of ionic ratios is crucial to identify their potential sources (Gopinath et al. 2016; Elumalai et al. 2023).

Identification of the source of calcium and bicarbonate ions in groundwater was carried out using the ratio of Ca²⁺ versus graph. If Ca²⁺ vs. ions in groundwater originate from calcite, the dissolved equivalent ratio of Ca²⁺ vs. would be 1:2; while a ratio of 1:4 explains the weathering of dolomite minerals (Subramanian et al. 2010). Accordingly, most of the water sampling points decreased almost close to the 1:2 line, showing that calcite predominates over dolomite as the calcium and bicarbonate ion source (Figure 9(b)).

Moreover, the Ca²⁺ + Mg²⁺ vs.TZ⁺ (total cations) scatter diagram was applied to prove the significance of silicate weathering. Figure 9(c) shows that the majority of water samples fall around the 1:1 equiline; this reveals that Ca²⁺ and Mg²⁺ ions originate from the weathering of carbonate rocks. Some points fall close to 0.6:1 line indicating the presence of partial silicate weathering in addition to carbonate rocks but is not a major source (Subramanian et al. 2010).

The Na⁺ + K⁺/total cation ratio can also be used to identify the cations produced by silicate minerals in groundwater (Stallard & Edmond 1983). The scatterplot of Na⁺ + K⁺ vs. TZ⁺ (Figure 9(d)) shows that most water samples fall above the 1:2 near TZ⁺, which reveals that fewer silicate minerals were dissolved in the process. Only a few samples fell near the 1:2 line, suggesting that while the carbonate rocks are the predominant sources, silicate weathering is also significant.

Moreover, the ratio of calcium to magnesium was used to determine the origin of calcium and magnesium. In the molar ratio of calcite to dolomite (Ca²⁺/Mg²⁺), pure dolomite weathering is to be expected at a ratio is 1:1, whereas; if the ratio is between 1 and 2, calcite weathering is to be expected. On the other hand, if the molar ratio is >2, the weathering of silicate minerals is taken into account (Mayo & Loucks 1995). According to Figure 10(b), most of the water samples are scattered above the 2:1 line, revealing that calcite weathering is the dominant process, followed by dolomite weathering as the source of these cations (Ayşen & Burcu 2021).

The relationship between and Cl⁻ and the correlation between and Cl⁻ allows for the identification of anthropogenic activity influences on groundwater chemistry (Subramanian et al. 2010). If anthropogenic processes control water chemistry, the correlation of nitrate versus chloride and sulfate versus chloride should be strong. Figure 10(c) and 10(d) show that anthropogenic activities have a smaller influence on the hydrogeochemistry of the present study area.

The main reason for the excess of Ca²⁺ or Mg²⁺ in water could be caused by the exchange of Na⁺ in the water with Ca²⁺ or Mg²⁺ from clay particles, while too much Na⁺ in groundwater could be caused by the exchange of Ca²⁺ or Mg²⁺ from the water with Na⁺ from clay minerals (Cartwright et al. 2007).

Ion exchange processes can be identified from the plot of Ca²⁺ + Mg²⁺ versus + ⁠. Under normal conditions or processes, ion exchange causes the points to shift to the right due to excess + ⁠, while reverse ion exchange results in points shifting left side owing to excess Ca²⁺ + Mg²⁺ (Srinivasamoorthy et al. 2012). Accordingly, as shown in Figure 9(a), almost all points shift to the left and are plotted above the equiline toward Ca²⁺ + Mg²⁺, indicating that a reverse ion exchange process is typical.

The present study focused on characterizing the hydrogeochemical process of groundwater in a mountain-bounded geologically complex setting. This provided a better understanding of the groundwater hydrogeochemical characteristics of low-grade basement rock and examined the appropriateness of the groundwater quality for drinking purposes. The findings revealed that the groundwater chemistry of the catchment is characterized by the dominance of calcium, bicarbonate and sulfate ions.

The hydrochemistry examination of the groundwater samples suggested that the Ca–Mg–SO₄–HCO₃ and Ca–SO₄–HCO₃ types of the groundwater are the most prevalent ones. The groundwater chemistry is changing from Ca–Mg–SO₄–HCO₃ dominant water types in the mountainous area to Ca–Na–HCO₃–SO₄ in the flat plains. The cation exchange mechanism with prolonged interaction between the water and rocks in the direction of the groundwater flow explains the process. Hydrochemical data showed that dissolution of calcium carbonate and gypsum, weathering of silicate minerals and ion exchange process are responsible for the nature of groundwater chemistry in the area.

Anthropogenic activity is not a significant influencing factor for groundwater chemistry. Nevertheless, the analyzed water samples showed that 46.6% for TDS, 46.6% for EC, 60% for TH, 80% for TA, 60% for Ca²⁺, 6.67% for K⁺ and 60% for of the water samples were above the permissible limit set by WHO. The interpolated spatial variation map of physicochemical parameters indicated that TDS, TH, Ca²⁺, Mg²⁺, and have almost similar trends in almost all locations, indicating geogenic sources.

Ultimately, the evaluation of the groundwater quality reveals that the water in certain areas of the research is unsuitable for drinking purposes. Hence, this study represents a warning for the local authorities providing significant insights to delineate a successful policy for the management of groundwater resources. Besides, the policymakers can benefit from the helpful information provided by the classification and source identification of dissolved ions in groundwater, which can help ensure the sustainable management of these essential resources.

Furthermore, since the study's findings indicate that boreholes drilled in lowland and floodplain areas are more likely to be contaminated than those drilled in highlands, groundwater quality control methods like drilling in some higher areas rather than lowland and floodplain areas can be implemented. In addition, the authors suggest that a detailed investigation of hydrogeochemical modeling and water resources monitoring in the research region should be carried out based on the stable water isotope ratio of oxygen in conjunction with stable carbon isotopes.

The authors thank Axum University and Mekelle University for the research support. The IIE Scholar Rescue Fund and Jackson School of Geosciences are acknowledged for supporting Tewodros Alemayehu's research stay at the University of Texas at Austin. Finally, the authors are grateful for the constructive comments and suggestions of the two anonymous reviewers for improving the manuscript.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.