Modeling megech watershed aquifer vulnerability to pollution using modified DRASTIC model for sustainable groundwater management, Northwestern Ethiopia

Ensuring access to improved sources of water and safe drinking water for all has been the Nation's concern. Groundwater is one of the valuable sources of freshwater. However, groundwater resources especially in shallow aquifers are susceptible to contamination. In this regard, the quality of groundwater in the study watershed has deteriorated due to industrial effluents and domestic wastes of Gondar city, and extensive use of fertilizers for agriculture purpose. Once the groundwater gets polluted, treatment is very difficult and expensive. Therefore, the most effective and realistic solution is to protect groundwater from contamination. Assessing the level of groundwater vulnerability is crucial for effective groundwater management. With this in mind, the aim of this study is to assess the aquifer vulnerability of Megech watershed to pollution using modified DRASTIC model. The modified DRASTIC model uses eight attributes including, depth to water table, net recharge, aquifer media, soil media, topography, impact of vadose zone, land use land cover, and hydraulic conductivity of aquifer. These layers were integrated using Raster calculator tool in a GIS environment. Fifteen groundwater composite samples were also collected and used to validate the model. The results of vulnerability analysis reveal that more than 85% of the groundwater of the study watershed is under medium to high vulnerability to water pollution. Aquifers highly vulnerable to pollution (5.74%) are mainly found in urban areas while majority of the aquifers (80.34%) which are moderately vulnerable are dominantly found in the cultivated lands. In the highly vulnerable part of the aquifer, the concentration of nitrate (17/mg) and total coliform (21/mg) exceeded WHO permissible limit which agrees with the vulnerability map. Effective management of groundwater resources has now become a critical issue. Thus, the study will be helpful for the proper management and protection of the available groundwater resources in the study watershed.