SACNASP CPD EVENT

"Central Branch Chair Dr Amy Allwright in interview with Dr Hansen after his presentation.."

ABOUT THE TALK Environmental groundwater risk assessments are required to be conducted for all new mining projects as well as expansion projects on existing mine sites. An important part of these risk assessments is the geochemical specialist study, which informs the groundwater assessment on pollution source terms and rates of contaminant release. The latter is especially applicable to post-closure environmental risk assessments. The mobility of potential pollutants in the groundwater system is an important consideration in the geochemical specialist study. For this purpose, the partitioning of potential pollutants in the groundwater between the groundwater solution and the solid phase is crucial to the realistic assessment of short- and long-term environmental risk.

The mobility of a potential pollutant is dependent on the solubility of solid phases, i.e. secondary minerals, it may form from the groundwater solution. It is also dependent on the sorption of these pollutants to solid organic and inorganic solid phases. To account for the sorption effect, risk assessments generally use the distribution coefficient parameter, i.e. Kd. Although the Kd can be used to assess pollutant mobility, it is only accurate at the laboratory conditions for which the Kd value was determined. Any natural variation in groundwater chemistry and physico-chemical parameters increases the uncertainty around the Kd value used significantly, to a point where it may no longer be applicable to the system being considered. One solution is to determine laboratory Kd values for specific pollutants of interest at a variety of conditions. However, this method is time-consuming and costly and the Kd values will only be applicable for the conceived conditions for which these values were determined. Another option is to use surface complexation theory to model pollutant sorption behaviour. Surface complexation theory allows changes in sorption due to changing physical conditions as well as changes in groundwater composition as a function of time and space. This method more accurately accounts for sorption behaviour in addition to the other geochemical processes, e.g. dissolution, precipitation and microbial catalysis of reactions.

ABOUT THE SPEAKER  Robert holds a PhD degrees in geology and specialises in geochemical modelling risk assessments from mineral waste and has 15 years of relevant experience. He has worked on a number of greenfields and brownfields projects in South Africa and Africa and internationally. He started his career at the Council for Geoscience, wherafter he moved to an environmental consulting firm where he was associate and specialist geochemist. He joined the University of the Free State in 2016 and is currently the Director of the Centre for Mineral Biogeochemistry.

Tuesday, Jun 1 @ 2:00 pm - 3:00 pm at Online Zoom event Dr Robert Hansen shares on this very topical issue. Environmental groundwater risk assessments are required to be conducted for all new mining projects as well as expansion projects on existing mine sites. An important part of these risk assessments is the geochemical specialist study, which informs the groundwater assessment on pollution source terms and rates of contaminant release.

Q&A

Hi Robert, thank you very much for the presentation, really informative. How conservative is SO4 in transport modelling. As a general rule, SO4 is used a worst case scenario in contaminant transport but under reducing conditions it is not conservative and most systems are..
14:31:52 From ockies : Thank you

Your comments regarding GNR635? How realistic is this and chances for changes..?

National Chairperson: Mr Fanus Fourie
Vice-Chairperson: Ms Nicolette Vermaak
National Treasurer: Mr Yazeed van Wyk
National Secretariat: Dr Jaco Nel
National Coordinator: Ms Elanda Schaffner

Please contact this Committee via [email protected]

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