Shallow groundwater zones are typically the most vulnerable to contamination from urbanization, population increase, agricultural practices and improper sewage disposal especially in developing areas. Shallow groundwater zones constitute the major source of domestic water supply to Dadin Kowa and its environs. The combined use of DRASTIC model and GIS was used for this study. Seven thematic maps of the DRASTIC model were developed in order to assess the vulnerability of groundwater to contamination and these include; depth to water table (D), recharge (A), aquifer media (A), soil media (S), topography(T), impact of vadose zone(I) and hydraulic conductivity(C). GIS was used to create an integrated map of the study area to delineate vulnerable zones. The DRASTIC index (DI) was computed based on a range of values. The final output was divided into three vulnerability zones, these are; 55-82 as low vulnerability, 82-110 as moderate vulnerability and 110-137 as high vulnerability zones to contamination. The results shows that low vulnerability zones occurred at the eastern part covering a percentage area of 30.3%, moderate vulnerability zones occurred at north-west and southern parts covering an area of 59.3% and high vulnerability zones scattered at the south western part of the study area covering 10.3%. These suggest that boreholes drilled at the high vulnerability zones are susceptible to contamination than areas of low and moderate vulnerability. Finally the validation of this model DRASTIC was done by comparing a categorized TDS map of the study area which are in agreement with the Vulnerability Index map.
Key words: DRASTIC, GIS, Groundwater contamination, Vulnerability, susceptible
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