GOD - and DRASTIC - based valuation of groundwater vulnerability to contamination of hinterland aquifers of northern part of Akwa Ibom State, Nigeria

There are growing worries over groundwater contamination globally. The main aim of this study is to evaluate the groundwater vulnerability to contamination in the northern part of Akwa Ibom state, southern Nigeria through the application of the GOD and DRASTIC models in conjunction with the surface electrical resistivity method. The results from the VES data interpretation acquired at 55 communities in the study region were utilized to appraise the groundwater vulnerability to contamination in the region. A maximum of 4 earth layers comprising sequence of sands (fine, coarse and gravelly sands) with minor clay intercalations were revealed by the sounding results. The aquifer layer exists at a depth ranging from 1.0 to 47.8 m and has a thickness of 18.6 to 102.7 m. The GOD model results show five groundwater vulnerability to contamination gradings (GWCG): very low (18%), low (25%), average (16%), high (29%) and very high (11%). The DRASTIC model results identity three GWCGs: low (33%), moderate (62%) and high (5%). The sensitivity analysis of the DRASTIC model reveals that the depth to the groundwater and hydraulic conductivity parameters have the greatest and least influence respectively on the GWCGs. The GWCG maps produced based on the GOD and DRASTIC models seems to show some degree of correlation and the respective grading areas are well demarcated. It is adjudged from these maps that the groundwater vulnerability to contamination grading is low, moderate and high respectively and these grading areas are well delineated on the maps. These outcomes provide a useful baseline data on groundwater contamination in the area which is essential for efficient and sustainable groundwater utilization in the region and other places with comparable geology.