Assessment of groundwater vulnerability in Webuye Municipality, Kenya

Access to safe water and sanitation is a basic human right and is enshrined in the sustainable development goal 6. Consequently, resources have been channeled towards development and improvement of water sources. Unlike surface water, the demand for groundwater is increasing due to its preserved quality, affordable development capital and drought resilience. Population density has resulted into entry of pollutants into aquifers because of reduced distance between the pollutants and groundwater sources, human activities and hydrogeological conditions. The aim of this study was to carry out an assessment of groundwater vulnerability to contamination as a preventive approach. Webuye town is a service area of Nzoia Water Services which provides water and sewerage services. However, water and sanitation coverage in Webuye town still below 50%, a portion of residents rely on onsite sanitation systems and groundwater. This is due to costs of installation, topographical challenges and limited pipeline extensions. It was observed that areas where groundwater sources are predominantly used, human waste is managed onsite close to groundwater abstractions points. The methods used in this study included the application of DRASTIC model which was interfaced in ArcGIS version 10.3. Inverse distance weighted (IDW) interpolation technique was used to produce vulnerability maps. The model inputs were seven: depth, recharge, aquifer, soil properties, topography, impact of the vadose zone, hydraulic conductivity and Land use. The results show that North Eastern areas of the study area; Maraka (Township) and Muchi scored the highest DRASTIC-LU values, implying high chances of groundwater vulnerability to contamination. The shallow water table, groundwater recharge, the type of soil, slope and the land use activities in the study area resulted into increased vulnerability. The findings should inform the municipality management on water quality precautions to be undertaken while developing groundwater sources in the area and development of pollution control framework.