Authors: Amissah, NBK; Addo, W; Sam, IA, Sutton, MW; Williams, M

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Amissah, NBK, Addo, W, Sam, IA, Sutton, MW & Williams, M 2013, 'Geochemical risk assessment of mine tailings to optimise closure strategy designs', in M Tibbett, AB Fourie & C Digby (eds), Mine Closure 2013: Proceedings of the Eighth International Seminar on Mine Closure, Australian Centre for Geomechanics, Cornwall, pp. 81-95,

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Gold mining in Ghana has, in several instances, involved significant environmental impacts, including heavy metal contamination of soils, water and food, with attendant risks to ecological systems and human health. A key aspect of impact mitigation following mine closure is the implementation of appropriately protective rehabilitation measures. At AngloGold Ashanti’s Iduapriem mine, a formal risk assessment (RA) approach has been adopted to ensure that mine closure strategies are designed in a manner fully commensurate with the prevailing environmental and toxicological risks. This paper describes this approach with respect to the Interim Tailings Storage Facility (ITSF), which was used for tailings storage from 2009 to 2011. Numerical risk assessment modelling for the ITSF was preceded by the development of a conceptual site model to elucidate all pathways by which communities or individuals may be exposed to deleterious elements derived from the ITSF and to characterise lifestyle, occupational, dietary, cultural and social factors that may directly or indirectly influence human contaminant exposure. In subsequent numerical RA modelling, all source-pathway-receptor linkages were parameterised (quantified) to yield multiple pathway exposure estimates for selected communities. This was undertaken using the RA code RISC5, a model that functions by calculating carcinogenic risk for any given human dose of contaminants of concern through comparison against a slope factor defined clinically or experimentally to express the relationship between intake of individual contaminants and carcinogenesis. Two scenarios were simulated to represent (a) current contaminant exposure levels among residents in local community areas and (b) exposure levels that could potentially arise in response to uncontrolled exposure to contaminants at levels prevailing at the ITSF source. Carcinogenic and non-carcinogenic risk quotients were calculated by comparing model outputs against reference doses from the US IRIS database. Incremental risks associated with long-term exposure to contaminants from the ITSF (in the absence of any active rehabilitation) were then calculated as the difference between risk factors for the two scenarios. Results of the numerical risk assessment show excess lifetime cancer risk probability of 1 case in 10,000 currently prevails in communities at Iduapriem as a consequence of ambient concentrations of arsenic (As) exposure. However, this risk is not attributable to the ITSF, in which As is present at concentrations of 1–2 mg/kg in tailings. The incremental non-carcinogenic risks associated with the ITSF are indicated by RISC5 to be negligible for all contaminants with the possible exception of lead.

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