Intrinsic groundwater pollution vulnerability assessment of Masama east well field, Khurutshe area

Abstract

An intrinsic groundwater pollution vulnerability assessment was conducted in Masama east well field, Botswana. The well field is located in close proximity to residential and agricultural land and might be exposed to the risk of groundwater pollution. The DRASTIC index model was applied to assess the groundwater pollution vulnerability of the study area. The technique combined a series of mathematical equations, physio-chemical properties of the study area and GIS to produce the standard groundwater pollution vulnerability map. The map was then calibrated using the sensitivity analysis to reduce the subjectivity associated with the DRASTIC index model and increase its accuracy. Additionally, the land use parameter was incorporated into the calibrated DRASTIC map to reflect the direct impact of human activities on the environment. These adjustments resulted in the production of the groundwater pollution vulnerability map of Masama east well field. This map was classified into four groundwater vulnerability classes labeled very low, low, moderate and high groundwater vulnerability. The very low, low, moderate and high groundwater vulnerability zones accounted for 39.0%, 19.9%, 27.5% and 13.6% of the total study area, respectively. Model validation was achieved using the spearman rank correlation coefficient and by visually comparing the nitrate distribution map of the study area and the land use map. The outcome of this study can be utilized as a guide by the land use planners, decision makers and the general public to divert activities that present greater risk of groundwater pollution to low vulnerability zones and preserve the water quality in the well field.