Improved Methods for Determining Soil-Atmosphere Flux Boundary Conditions at Mine Waste Repositories

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Successful operation and closure of mine waste repositories require accurate quantification of the surface water budget that controls the infiltration of meteoric water into the waste profile. The rate of net surface infiltration ultimately generates internal seepage with the release of potential leachates that may threaten downstream receptors. Recent field scale observations at both active and reclaimed mine sites in Canada, as well as international sites operated by Canadian companies, have shown current predictive models used to calculate infiltration rates for mine waste deposits such as waste rock dumps and tailings impoundments are unacceptable. For example, net infiltration rates determined directly on the basis of measured flow rates in the drainage collection ditches at Equity Silver mine in British Columbia have been found to be three fold greater than infiltration rates predicted using the current soil-atmosphere modelling methodology. The global objective of the research program proposed here is to investigate the reasons for these errors and to improve the existing soil-atmosphere methods currently available for estimating surface flux boundary conditions at mine waste repositories.