Modeling Groundwater vulnerability to pollution on the Southern slopes of Kilimanjaro, Tanzania

Abstract

The vulnerability of groundwater to contamination risks can be primly linked to unchecked impacts of anthropic activities in most potential groundwater areas. The Kahe aquifer, located on the southern slopes of Kilimanjaro, is increasingly threatened by such activities. This study assessed the contamination risks associated with groundwater using the land use DRASTIC approach in a GIS environment. The approach entailed integrating eight influencing factors: depth to groundwater, net recharge, aquifer media, soil media, topography, the impact of the vadose zone, hydraulic conductivity, and land use/cover. These factors were processed and analyzed in a geospatial database to generate a groundwater Vulnerability model. The model revealed that the most vulnerable areas are concentrated in zones with high anthropogenic activities. This high vulnerability is primarily due to several contributing factors: a shallow water table, gently sloping terrain, the presence of alluvial formations, and the unconfined nature of the aquifer. We found a strong correlation, as most vulnerable zones were found to coexist with elevated nitrate levels, a key indicator of pollution. These findings are useful as they provide critical data for policymakers and water resource managers. The study highlights the urgent need for immediate and long-term protection measures in highly vulnerable areas and provides a foundation for refining groundwater management policies and strategies. The model and its results can be used for upscaling existing policies, prioritizing management efforts, and implementing immediate mitigation strategies to abate contamination risks and protect groundwater quality for the future.