Application of multivariate statistics in the analysis of groundwater geochemistry in and around the open cast coal mines of Barjora block, Bankura district, West Bengal, India

Inappropriate environmental management systems of open cast coal mines (OCCMs) often become a potential threat to aquifers, specifically unconfined alluvium aquifers. The present study area, a part of lower Gondwana coalfield, is an example of upper alluvium unconfined aquifer with shallow water table and lower multi-layered confined aquifers. Multivariate statistics has been effectively used as an aid to interpret different hydrogeochemical parameters to identify the prospective risk from OCCM and probable reasons responsible for variability in groundwater chemistry. Factor analysis has been used to identify the possible factors that control the variability of various chemical parameters in both pre-monsoon and post-monsoon times. Natural hydrogeologic environment (factor 1) is the major factor causing 53.34% and 51.01% of total groundwater-quality variation in post- and pre-monsoon times, respectively. In post-monsoon season, 13.33% variability is caused by anthropogenic activity (factor 2). Cluster analysis classifies 46 post-monsoon groundwater samples in three groups (clusters). Cluster 3, representing worst water qualities among the three clusters, has been significantly found in close proximity to the mines. ANOVA one-way analysis of cluster 3 groundwater samples shows higher concentration of TDS, Ca, Na, Cl, HCO_3, and lower pH value in post-monsoon season than pre-monsoon season. Weathering and leaching of silicate minerals present in mine tailings and/or spoils by rain water may be the possible reason for degrading quality of groundwater. If this trend continues, then groundwater may become alkaline in nature with high (Na + K) concentrations in the long run, as indicated by Piper plot of all clustered samples.