Groundwater Pollution Potential Index (GWPPI) as a Tool for Vulnerability Study of Coastal Plain Sand Aquifers of Calabar, South Eastern Nigeria

Abstract

The work documents a vulnerability study of coastal aquifers based on Groundwater Pollution Potential Index (GWPPI). The parameters used in GWPPI include Lithofacies (L), aquifer thickness (b), Transmissivity (T), Storativity (S), Static Water Level (SWL), Total Dissolved solids (TDS), Chloride (Cl-), Nitrate (N03-) and Escherichia coli (E-coli). GWPPI is computed as the sum of the products of weights and ratings assigned over all the parameters. The GWPPI varies between 27 and 56 is divided into three classes; High (>40) Medium (30-40) and Low (<30). The results show that the most vulnerable areas are located in the southern part (zone 3) of the study area (GWPPI>40) which are mostly influenced by the nearness of SWL to the ground surface and biochemical pollution indicators (E-coli, NO3-, Cl-). The correlation matrices of parameters show moderate positive correlation between E-coli and No3- (r=0.642) and moderate negative correlation between E-coli and SWL (r=-0.624). The coastal aquifer is thus affected mostly by the influence of anthropogenic (human) activities based on the concentrations of NO3- (0.43–10.25 mg/l) and E. coli (1-50 counts/100 ml) in ground water than geogenic factors. GWPPI can be applied not only to Coastal Plain sandy environment but other sedimentary basins with similar conditions.