Hydrogeological framework of the volcanic aquifers and groundwater quality in Dangila Town and the surrounding area, Northwest Ethiopia

Volcanic aquifers are sources of groundwater for both urban and rural areas. Their occurrence in geological formations and water quality are the main issues for sustainable utilisation. Dangila town and its surrounding area, northwest Ethiopia, is assessed for hydrogeological framework and groundwater quality based on well and hydrochemical data. The study showed that the area has a multi-aquifer system: an unconfined perched aquifer at shallow depth and; semi-confined and confined aquifers at greater depth in Quaternary basalts. The aquifer has five groundwater facies: Ca-HCO3, Ca-Mg-HCO3, Ca-Na-HCO3, Na- Ca-HCO3 and Na-HCO3. The Ca-HCO3 groundwater types are dominant in the shallow unconfined aquifer system, and the Na- Ca-HCO3 and Na-HCO3 types are dominant in deep aquifer systems. Mixing of waters from shallow and deep aquifer systems is minimal and possible only through interconnected fractures. Groundwater storage and flow is controlled by intensity and interconnection of fractures. Hydraulic conductivity is higher for fracture dominant aquifers than weathered rock aquifers. The groundwater chemistry is mainly controlled by rock weathering and cation exchange. Groundwater quality assessment shows that water from both aquifer sources is potable. Based on sodium adsorption ratio (SAR) and residual sodium carbonate (RSC) values, all groundwater schemes are in the excellent quality class and can be used for irrigation without any problem. However, high Na+ in borehole samples restrict the deep groundwater suitability for irrigation use without adjustment. The combined results of the study are used to construct a hydrogeological conceptual model of volcanic aquifers, which can be used to manage the groundwater resource for sustainable development. This study would be helpful for water resources management in other similar geological settings.