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.

Trihalomethanes (THMs) are toxic disinfection by-products, formed in the reaction of chlorine with organic matter. This work aimed to study THM formation during a unique case study of managed aquifer recharge (MAR) with chlorinated desalinated seawater. THM formation was tested in the field, along a 3.0 m deep vadose zone gallery. Two small-scale experiments were conducted in the site, with untreated and with bromide spiked desalinated seawater. These were accompanied by a large-scale, ~1-month long operational MAR event. In the small-scale experiments, THM concentrations were shown to increase with bromide concentrations, with increasing dominance of the brominated species. Nevertheless, concentrations remained within the single µg/L range, which is an order of magnitude lower than drinking water regulations. Such low THM concentrations were also determined in the large-scale event. In both cases, THM formation occurred in the ponding water, without significant formation or degradation in the upper 3.0 m of the vadose zone. This study shows that MAR with chlorinated (<0.5 mg/L) desalinated seawater through sandy infiltration basins does not pose a threat to drinking water quality at this site.

Rationale: Chloroform, a probable human carcinogen, is commonly detected in various concentration levels in many surface water and groundwater sources. Compound‐specific chlorine stable isotope analysis (Cl‐CSIA) is significant in investigating the fate of chlorinated contaminants in the environment. Analytical conditions should, however, be thoroughly examined for any isotopic fractionation. In this study, we simultaneously optimize three analytical parameters for a robust online Cl‐CSIA of chloroform using the Taguchi design of experiments. Methods: For Cl‐CSIA, a purge‐and‐trap autosampler coupled to a gas chromatograph in tandem with a quadrupole mass spectrometer, with electron ionization in selected ion monitoring (SIM) mode, was used. Using the Taguchi method, the dominant parameter affecting the results of Cl‐CSIA for chloroform was identified through concurrent investigation of the signal‐to‐noise ratios (S/N) of three parameters, each at three levels: purging time (5, 10, 15 min), transfer time (80, 120, 160 s), and dwell time (20, 60, 100 ms). Moreover, the optimum combination of the levels was identified. Results: The purging time, with a maximum S/N, resulted in the highest influence on the isotope ratios determined. It was further refined through additional experiments to sufficiently extract chloroform from the aqueous phase. Accordingly, 8 min of purging time, 120 s transfer time and 100 ms dwell time were the optimum conditions for Cl‐CSIA of chloroform. Post‐optimization, a precision of ±0.28 ‰ was achieved for 8.4 nmol of chloroform (equivalent to 0.89 μg or approx. 25 nmol Cl‐mass on column). Conclusions: A simple online method for Cl‐CSIA of chloroform was optimized with the Taguchi design of experiments. The Taguchi method was very useful for the optimization of the analytical conditions. However, the purging conditions should be fine‐tuned and selected so that sufficient extraction of a target compound is confirmed to acquire a stable and higher precision of the method.

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.