The management and monitoring of the quality of water resources in the Mekelle area are challenging, due to both geogenic and anthropogenic impacts. The extent of these impacts and the sources of pollution in this area have not been thoroughly investigated. In this article, a mapping of water resources vulnerability was carried out using the DRASTIC method and a modified DRASTIC vulnerability map was produced. Single-parameter and map-removal sensitivity analyses were performed on the relevant rates and weights. A final DRASTIC vulnerability index, varying from 54 to 140, was divided into four vulnerability classes: low (225.7 km²), medium (302.8 km²), high (307.2 km²), and very high (187.6 km²); the values in the parentheses indicate the corresponding areal coverage of each class. Similarly, a modified DRASTIC vulnerability index, ranging from 91 to 192, was divided into four vulnerability classes: low (166.4 km²), medium (266.8 km²), high (338.0 km²), and very high (252.2 km²) Nitrates were used to validate both models. in which moderate positive correlations (with Pearson’s correlation coefficient, r) of 0.681 and 0.702 were calculated for the DRASTIC and modified DRASTIC indices, respectively. A comparison of the two maps showed that significant sources of pollution are located in areas with high to very high vulnerability. The results of this research work can be used for the protection and monitoring of groundwater resources in the Mekelle area.

This study provides a comprehensive analysis of the groundwater potential of hard rock aquifers in five diverse African case study areas: Lake Tana Basin and Beles Basin in northwestern Ethiopia and Mount Meru in northern Tanzania (comprising volcanic aquifers); the Mekelle area in northern Ethiopia and Jifarah Plain in Libya (consisting of sedimentary aquifers). The evaluation of recharge, transmissivity, and water quality formed the basis of qualitative and quantitative assessment. Multiple methods, including water table fluctuation (WTF), chloride mass balance (CMB), physical hydrological modeling (WetSpass), baseflow separation (BFS), and remote sensing techniques like GRACE satellite data, were employed to estimate groundwater recharge across diverse hydrogeological settings. Topographic contrast, fractured orientation, lineament density, hydro-stratigraphic connections, hydraulic gradient, and distribution of high-flux springs were used to assess IGF from Lake Tana to Beles Basin. The monitoring, sampling, and pumping test sites took into account the high hydromorphological and geological variabilities. Recharge rates varied significantly, with mean values of 315 mm/year in Lake Tana Basin, 193 mm/year in Mount Meru, and as low as 4.3 mm/year in Jifarah Plain. Transmissivity ranged from 0.4 to 6904 m²/day in Lake Tana Basin, up to 790 m²/day in Mount Meru’s fractured lava aquifers, and reached 859 m²/day in the sedimentary aquifers of the Mekelle area. Water quality issues included high TDS levels (up to 3287 mg/L in Mekelle and 11,141 mg/L in Jifarah), elevated fluoride concentrations (>1.5 mg/L) in 90% of Mount Meru samples, and nitrate pollution in shallow aquifers linked to agricultural practice. This study also highlights the phenomenon of inter-basin deep groundwater flow, emphasizing its role in groundwater potential assessment and challenging conventional water balance assumptions. The findings reveal that hard rock aquifers, particularly weathered/fractured basalt aquifers in volcanic regions, exhibit high potential, while pyroclastic aquifers generally demonstrate lower potential. Concerns regarding high fluoride levels are identified in Mount Meru aquifers. Among sedimentary aquifers in the Mekelle area and Jifarah Plain, limestone intercalated with marl or dolomite rock emerges as having high potential. However, high TDS and high sulfate concentrations are quality issues in some of the areas, quite above the WHO’s and each country’s drinking water standards. The inter-basin groundwater flow, investigated in this study of Beles Basin, challenges the conventional water balance assumption that the inflow into a hydrological basin is equivalent to the outflow out of the basin, by emphasizing the importance of considering groundwater influx from neighboring basins. These insights contribute novel perspectives to groundwater balance and potential assessment studies, challenging assumptions about groundwater divides.

Water quality degradation is one of today's key environmental challenges. Once contaminated, its treatment becomes difficult and prohibitively costly. Therefore, efficient and sustainable groundwater management is essential to conserve this vital resource. This is particularly true for the Elalla-Aynalem catchment, which serves as the primary water source for Mekelle town. This study aimed to produce optimized maps of groundwater table depths and nitrate concentrations using geospatial models, based on 123 data points for groundwater levels and 71 data points for nitrate concentrations. Empirical Bayesian Kriging (EBK) proved to be the most effective interpolation technique for groundwater table depth, while Simple Kriging (SK) was the best choice for predicting nitrate concentration, as determined by the lowest root mean square error (RMSE). The ranking of interpolation models for groundwater table depths was EBK > SK > OK > UK > IDW > RBF > LPI, whereas for nitrate concentrations, the models ranked as SK > EBK > IDW > OK > UK > RBF > LPI. These results demonstrate that geostatistical methods outperformed deterministic interpolation techniques for both parameters. The northwest and central regions of the study area were found to have shallow groundwater table depths, areas that also exhibited high nitrate concentrations, likely due to their proximity to pollutant sources. This research provides valuable insights for promoting sustainable groundwater exploration and implementing effective measures to protect groundwater from contamination.

This study aimed to investigate the shallow groundwater status around the Sheba Leather Tannery area, Wikro, North Ethiopia, through geophysical and hydrochemical methods. Seventeen Vertical Electrical Soundings (VESs) acquisitions, 4 upstream and 13 downstream, of the leather tannery area were conducted. Using the data, four geoelectric profiles were generated. The aquifers’ geoelectrical layers, depth, and lateral extent were delineated. The VES curves depicted three to four resistivity layers. These alternating layers of low, moderate, and high resistivity values, traced at different VES points, were attributed to the formations’ composition and the groundwater quality status. Besides the geophysical survey, 32 water samples were collected from the area. Parameters such as electrical conductivity (EC), total dissolved solids (TDSs), pH, major ions, and heavy metals were analyzed. Moreover, PHREEQC was used to determine the groundwater mineral saturation indices where most minerals, except halite, were found supersaturated. The quality status for drinking purposes was also evaluated using the water quality index (WQI), and the water was classified as good (56.3%), poor (37.5%), and very poor (6.2%). The sodium adsorption ratio (SAR) and the percentage of sodium (Na⁺%) were calculated, and the results indicated that the water is suitable for direct use in irrigation.

Identification of recharge sources in the Mekelle area is controversial, as some studies indicate that precipitation is the only source of recharge, while others indicate the existence of inter-catchment/inter-basin groundwater transfers with the possibility of intermediate-to-regional flow system recharge sources. The objectives of this study were, therefore, to identify the sources of recharge, quantify the groundwater recharge and develop a local meteoric waterline (LMWL) for the Mekelle area using the stable isotopic compositions (δ¹⁸O and δ²H) of rainwater. To that end, 13 precipitation, 34 groundwater, and two surface water samples were analyzed for δ¹⁸O and δ²H signatures. Accordingly, the local meteoric water line (LMWL: δ²H = 6.78 δ¹⁸O + 9.83) was developed from ten monthly accumulated precipitation samples and three rainfall event samples. Moreover, the spatial variations in the isotopic compositions of the groundwater with respect to the LMWL showed the existence of three zones/groups with different groundwater flow conditions, namely, shallow, intermediate, and deep flow systems. Two groundwater recharge sources were also identified from the dual-isotope slope of the groundwater isotope lines with respect to the LMWL. Furthermore, the groundwater recharge was estimated to be 49 mm/year using the chloride mass balance (CMB) method.