Assessment of Spatial Variation of Groundwater Quality in a Mining Basin

Assessment of groundwater quality is vital for the sustainable safe use of this inimitable resource. However, describing the overall groundwater quality condition-particularly in a mining basin-is more complicated due to the spatial variability of multiple contaminants and the wide range of indicators found in these areas. This study applies a geographic information system (GIS)-based groundwater quality index (GQI) to assess water quality in a mining basin. The study synthesized nine different water quality parameters available-nitrate, sulphate, chloride, sodium, magnesium, calcium, dissolved mineral solids, potassium, and floride (NO3-, SO42-, Cl-, Na+, Mg2+, Ca2+, DMS, K+ and F-)-from 90 boreholes across the basin by indexing them numerically relative to the World Health Organization standards. The study compared data from 2006 and 2011. The produced map indicated a lower GQI of 67 in 2011 compared to 72 in 2006. The maximum GQI of 84.4 calculated using only three parameters (Mg2+, K+ and F-) compared well with the GQI of 84.6 obtained using all nine parameters. A noticeable declining groundwater quality trend was observed in most parts of the basin, especially in the south-western and the northern parts of the basin. The temporal variation between the GQIs for 2006 and 2011 indicated variable groundwater quality (coefficient of variation = 15-30%) in areas around the mining field, and even more variability (coefficient of variation >30%) in the south-western and eastern parts of the basin.