Investigation of hydrogeochemical processes in groundwater resources located in the vicinity of a mine process water dam

The study aims to identify and describe the dominant hydrogeochemical processes and their contribution to the overall groundwater quality of an aquifer situated in the vicinity of a mine process water dam. The study site is located in a typical Karoo Basin of Southern Africa. Groundwater samples were collected from a network of boreholes designed to monitor the migration of contamination from the mine process water dam during a five year period from November 2007 to November 2011. The study utilises the expanded Durov diagram, bivariate plots and correlation coefficients statistics to analyse groundwater chemistry data. Based on analyses of the groundwater chemistry the study area was divided into two hydrogeochemical zones; the fresh background and contaminated groundwater. Fresh water in the background aquifer is characterised by a Na+-HCO3- hydrochemical groundwater type. Groundwater in the contaminated zone comprises of Mg2+-Cl− and Na+-Cl−, two main hydrochemical water types. High levels of EC and TDS that ranges from 63.10 to 1870 mS/m and 690-11443 mg/l respectively were measured in the contaminated groundwater indicating that the aquifer has been affected by saline water from the dam. Major ions of Mg2+, SO42- and Ca2+ measured in the contaminated portion of the aquifer are positively correlated to the conservative Cl− indicating that these ions were derived from the same saline source (dam). The study identified albite dissolution as the main hydrogeochemical process responsible for the evolution of fresh groundwater chemistry in the background aquifer. The aquifer on the down gradient of the process water dam is contaminated by saline water that evolved from the dam. There is evidence to show that the mine process water dam poses a serious threat of contaminating the groundwater with salts. A recommendation was therefore made to the responsible authorities to consider decommissioning of the facility given that the mine operations ceased some years back.