Spatial analysis of groundwater vulnerability to contamination and human activity impact using a modified DRASTIC model in Elalla-Aynalem Catchment, Northern Ethiopia

Abstract

Once if groundwater has been contaminated, it is difficult to treat it since natural dilution is slow and artificial flushing is impractical. Hence, this study was aimed to analyse the spatial vulnerability to contamination and human activities impact on the groundwater of Elalla-Aynalem Catchment, using depth to water table, net recharge, aquifer type, soil media, topography, impact of vadose zone, hydraulic conductivity and land use/cover. DRASTIC index gives three different groundwater vulnerability zones, namely: high (6.7%), moderate (32%) and low (61.3%), and the modified DRASTIC (Human activity impact) index map gives four vulnerability zones as low, medium, high and very high with area coverage of 18.5%, 29.1%, 32.6% and 19.8% of the study area, respectively. The depth to water table and vadose media are the most significant hydrogeological factors determining the DRASTIC vulnerability resulted from sensitivity analyses. The groundwater vulnerability map with measured NO3 data shows 70.69% and 84.48% agreement for DRASTIC model and modified DRASTIC model, respectively, indicated that the role of LuLc is important. Solid waste disposal, sewerage, gases from industries, municipal wastes, garages, fuel station, health centers and agricultural activities are some of the possible pollutants that could continuously deteriorate the quality of groundwater in the catchment. This study provides integrated plat form and compressive data set of hydrogeological factors for spatial analysis to fill spatial data gaps, and it can be effectively utilized in the planning and management of the groundwater resources in vulnerable zones of Elalla-Aynalem Catchment.