Groundwater vulnerability assessment in degraded coal mining areas using the AHP-Modified DRASTIC model

Extensive coal mining results in ecological upheaval. Mining activities such as excavation and dumping of overburden convert land into new habitats, which completely degrades the soil structure. Adverse impacts of coal mining activities on water resources have been reported from several such regions. This study focusses on the assessment of groundwater vulnerability due to land degradation in coal mining areas. Three techniques were used to study the groundwater vulnerability: (a) the original DRASTIC overlay and index based model, (b) a modified DRASTIC model developed by adding land use and distance from lineament parameters, and (c) a model developed using analytic hierarchy process to optimise the rates and weights of the modified DRASTIC parameters. The groundwater vulnerability assessment models were validated by comparing the analysed groundwater samples data of the region and then by comparing with the computed overall water quality index for each sampling site. The results showed that groundwater vulnerability assessment in coal mining areas can be significantly improved. The best results were observed using an analytic hierarchy process-Modified DRASTIC model, which showed the highest positive significant (p<.01) correlation (r=.94) with the water quality index. Spatial distribution results revealed critical impact of land degradation due to coal mining on groundwater, as nearly 24% of the entire study area lied in the high to very high vulnerable zones, most of which are located in the vicinity of mining areas. This study will help in better water management practices in coal mining areas.