Water quality modelling and scenario analysis of the Leeuspruit River in support of the G4 closure process of Sigma Colliery

AR Slaughter, NJ Griffin and ON Odume
August 2022–January 2023

Sponsor: Sasol Mining

Sigma Colliery is a defunct coal mine that was operated by Sasol Mining (Pty) Ltd. It is situated to the north, west and south of Sasolburg in the Free State. Sasol is taking steps to close the Sigma Colliery. As a part of this process, potential impacts and mine water management considerations for mine closure need attention. The best practice guidelines (BPG) for this aspect of mine closure are the best practice guidelines of the Department of Water and Sanitation that use source-pathway receptor and risk-based approaches to mine water management. Sasol will have to comply with the outline requirements of the BPG G4 impact prediction and BPG G5 water management aspects for mine closure. The closure of Sigma Mine requires that water quality impacts on Vaal River Water are curtailed. Although the Leeuspruit carries a load of salinity (mostly as sulphates) and nutrients (most notably, as phosphate), previous surveys have found no impact of Vaal River water quality where the Leeuspruit joins the Vaal River. However, downstream assessments of Vaal River water quality (highway bridge over Vaal River) show decreased quality and there is concern that decant from Sigma Colliery may be responsible for this. In order that impacts are limited, we will model surface water quality in the Leeuspruit and Vaal Rivers to simulate water quality in the region. This would require modelling water quality in the Rietspruit (north bank) as this affects the Vaal River water quality. Finally, the water model will be used to assess the impact of mitigation through scenario analysis which will use a water quality model for the Vaal Barrage developed in the prior research project.

Last Modified: Wed, 14 Aug 2024 12:41:11 SAST