An environmental risk assessment framework for developing financial liability estimates for closing five abandoned metal mines in northern Saskatchewan, Canada

摘要

Public sector accounting standards require governments to estimate and report financial liabilities associated with contaminated sites for which they are responsible. Abandoned mines represent a large potential financial liability for governments, but it is difficult to quantify these liabilities accurately without investing significant monetary resources in environmental investigations at the sites. Additionally, without the benefit of a site-specific environmental risk assessment, liabilities may be booked on the basis of generic environmental quality criteria such as national or provincial soil, water and sediment quality guidelines or standards. However, these generic criteria were not intended to signal a need for clean-up, and their use in this context results in an overestimate of environmental risk and the associated financial liabilities. An environmental risk assessment framework was developed to assist in deriving estimates of financial liability for five abandoned hard-rock metal mines in northern Saskatchewan, Canada, for which there were limited existing environmental data. The framework accounts for potential risks to human health, plants and invertebrates, and fish and wildlife. Risks are estimated based on an evaluation of the potential magnitude, spatial extent and duration of exposure; the relative sensitivity of the exposed organism; and the relative potency and mechanism of toxicity of the contaminant. The framework is systematically applied to categorise potential human health and ecological risks associated with environmental contamination according to one of four possible outcomes: (1) low risk with low uncertainty in the conclusion; (2) low risk with high uncertainty in the conclusion; (3) high risk with high uncertainty in the conclusion; and (4) high risk with low uncertainty in the conclusion. Contamination associated with high risk and low uncertainty conclusions was considered an environmental liability, and cost estimates to manage the contamination were developed. Contamination associated with low risk and low uncertainty conclusions was not considered an environmental liability, and no cost estimates were developed. Risks with high uncertainty conclusions were identified as data gaps for further investigation. This presentation will use the five mine sites in Saskatchewan to illustrate the application of the environmental risk assessment framework and demonstrate its potential application to other contaminated mine sites for estimating financial liabilities and identifying relative priorities for further investigation or risk management.