Application of temporal GIS to track areas of significant concern regarding groundwater contamination

This study is intended to explain discrimination of permanent and temporary groundwater quality zones using temporal geographic information system. The test area for this work is Lahore, Pakistan, where both quality and quantity of underground aquifer are under pressure due to anthropogenic activities. The analysis has been performed after developing precise interpolated surfaces, and verified through cross-validation, for the quality parameters of pH, TDS, Ca, Mg, Cl and HCO₃. All the parameters have been studied from the year 2010–2013 for their individual as well as combined geographic distribution in the form of water quality index (WQI). Time series maps of individual parameters with same spatial scale have led the analysis to the extreme behavior of pH and Mg in the year 2011 and concentration of TDS crossing WHO limits in year 2010 (1323 mg/L), etc. Spatio-temporal analysis of WQI figured out temporary as well as permanent epicenters of groundwater pollution, the one around Anarkali region is not only permanent but also expanding gradually. On the basis of WQI scores, five categories have been introduced; WQI < 70 is “good,” 70 < WQI < 84 is “moderately good,” 84 < WQI < 97 is “marginally good,” 97 < WQI < 110 is “moderate,” and WQI > 110 is “poor.” It is found that categories attributed to “good” and “moderately good” are spatially transforming to “moderate” and “poor.” The results are endorsed by WQI for the year 2014, exhibiting the same contamination plume with an expansion rate even higher than the previous years. This study can be useful to channelize the limited resources of developing countries for preservation of existing aquifer.