Hydrochemical Characteristics of Open-Pit Groundwater from a Closed Metalliferous Mine in O'kiep, Namaqualand Region, South Africa

Abstract

Abstract-O'kiep, a small town located in the arid to semi-arid Namaqualand region of South Africa is dependent on the Lower Orange River for its water needs, i.e. for domestic and agricultural use. The protection of groundwater resources in this region is important due to water shortages with no peripheral rivers. The town is characterised by an environment with a high proportion of mine tailings and dumps containing sulfidic ores, which can facilitate groundwater contamination. As such, open-pit groundwater (OPGW) samples were collected downstream from a closed metalliferous mine and analysed for physicochemical properties, to evaluate the fitness of OPGW for any potential use. A charge balance error (%CBE) of ±5% was used to interpret the hydrochemical properties of the OPGW, with results indicating that the water is mildly acidic, with a high concentration of SO42-, which suggested sulphide oxidation and weathering of the exposed rocks. Overall, the OPGW was under saturated in terms of metallic species such as Sb, AS, Cd, Cr, Co, Hg, Ni, Se, V and Zn. Furthermore, when the hydrochemical determinants were compared to national drinking water guidelines, it was determined that the OPGW is not suitable for drinking nor irrigation thus requires treatment prior to utilisation.

Seasonal variation of hydrochemical characteristics of open-pit groundwater near a closed metalliferous mine in O’Kiep, Namaqualand Region, South Africa

“…This was attributed to natural seasonal groundwater table fluctuations (Rijal et al 2010). When the OPGW pH is low, the higher the mobility of Sb, As, Cd and CN − ; thus, mobilisation in the groundwater a phenomena linked to the geologic setting of the study area, which is further influenced by the geochemistry of the mine waste, mine tailings which contaminates the immediate environment in the study area (Erdogan et al 2017(Erdogan et al , 2018Moncho et al 2017). Additionally, geochemical processes controlled the mobilisation of Sb and As (Ramos et al 2014).…”

“…These processes that might control the ion enrichment are dissolution, redox, evaporation and the residence time, which promote water-rock interaction. Additionally, the study area, generally, has poor groundwater quality due to geogenic sources of chemical constituents; especially, PTEs (Erdogan et al 2017;Abiye and Leshomo 2013). The chemical composition of the OPGW indicated the dominance of the Na + and Cl − ions resulting in a Na-Cl water type and similar results were obtained by Nakwafila (2015).…”

“…Therefore, it was necessary to investigate the seasonal variation of the quality of an open-pit groundwater (OPGW) near a closed metalliferous mine. Earlier studies by Erdogan et al (2017), carried out in this area, evaluated the hydrochemical characteristics of the OPGW quality. However, these studies did not attempt to assess the seasonal variation in the OPGW quality.…”