Abstract
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.
Highlights
IntroductionSometimes the only, sources of groundwater in many regions of the world
Volcanic aquifers are vital, and sometimes the only, sources of groundwater in many regions of the world
Sometimes the only, sources of groundwater in many regions of the world. They are stored in volcanic rocks that are considered as minor in areal coverage of continental crust compared to other rock types
Summary
Sometimes the only, sources of groundwater in many regions of the world. They are stored in volcanic rocks that are considered as minor in areal coverage of continental crust compared to other rock types. The proportion of volcanic rocks exposed on continents totals only 6.8–8% of all the rock types of the earth (Blatt and Jones, 1975; Meybeck, 1987; Suchet et al, 2003) Among these extrusive rocks, 36% of the total is found between 0 and 30 N, mainly in the Deccan Traps in India, and in Ethiopia (Suchet et al, 2003). Owing to the complexity of volcanic rocks, the inadequacy of data and limited previous research, the hydrogeology of the area is barely understood
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