Application of GIS technique in suitability assessment of groundwater in the Assin North and South municipalities, Ghana

Abstract

The application of the GIS technique in the groundwater quality assessment of the Assin North and South Municipalities has been carried out to assess its suitability for drinking, domestic and irrigational uses. Data for this study was taken from the Community Water and Sanitation Agency office in Cape Coast. The World Health Organization (WHO) guidelines were used for the assessment of groundwater quality. The assessment of the irrigational water quality was based on Sodium Percentage, Sodium Adsorption Ratio, Residual Sodium Carbonate, permeability index, Magnesium hazard and Kelly index. The types of groundwater in the area include CaMgHCO3, mixed groundwater, NaCl, and CaMgSO4 based on the Piper diagram. The major factors controlling groundwater chemistry include rock weathering, ion exchange, and impacts of human activities. The groundwater is generally suitable for drinking and domestic purposes. However, some of the samples showed high concentrations of certain parameters including turbidity, NO3−, Mn, PO4, Fe, F−, EC, Cl−, and colour which make them unsafe for drinking without prior treatment in selected communities. The water quality index tool revealed that 29% of the groundwater samples are of excellent quality, 54% are of good quality, 10% are of poor quality, 2% are of very poor quality and 5% are unsuitable for drinking. It was observed that the communities within the middle zone of the study area have groundwater of poor quality compared to that of the extreme ends. The poor groundwater quality may be attributed to the impacts of anthropogenic activities including, galamsey, lack of hygienic conditions around boreholes, the use of pit latrine, and application of agrochemicals. Considering the irrigational use, the groundwater is generally suitable. However, about 20% show unsuitable quality based on magnesium hazard (MH), 5% show unsuitable quality based on Na%, 20% show suitable quality based on Kelly Index (KI) and 34% show corrosive groundwater type. Application of the Wilcox and the USSL classifications of irrigation water revealed that the groundwater is suitable for irrigational use. The study has revealed the effectiveness of integrating the GIS technique and hydrochemistry in the assessment of groundwater quality, spatial variation of the groundwater quality and processes affecting the groundwater chemistry and overall quality.