Heavy metal(loid) pollution of a hard-rock aquifer: evidence, distribution, and source

Composition of groundwater in the mining areas can be affected by oxidation of sulfide minerals and related reactions. Given that in the Miduk copper mine area, groundwater is the only available water resource for drinking and agriculture purposes. In the study area, assessment and measurement of groundwater physicochemical properties such as pH, TDS, EC, major cations, and major anions were performed. Physicochemical studies showed that the calcium and sulfate are the main cations and anions (Ca-SO₄ water type), respectively. Groundwater in the area is mainly fresh and with a source of meteoric water infiltration. Three pollution indices, HEI, HPI, and C_d, were selected to evaluate the concentration level of ten of heavy metal(loid)s (Al, As, Cd, Cu, Fe, Mn, Mo, Ni, Pb, and Zn). To investigate the source and relations between heavy metal(loid)s, multivariate statistical analysis was executed for eleven variables. The results of pollution indices showed that samples in group 1 (mine pit area) have the highest level of pollution and considering that the samples of this group are in the closest distance to the mine pit and group 3 (springs) around the study area had the least level of pollution. Multivariate statistical analysis showed a negative correlation between heavy metal(loid)s (with the exception of arsenic and molybdenum) with the distance from the mine pit. This suggested the origin of these elements can be considered as anthropogenic source due to mining activities. The geogenic source of arsenic, molybdenum, and lead can be cited based on Spearman's correlation coefficient supported by PCA analysis.