The British Columbia Human Health Risk Assessment Framework. R. C. Lee, Golder Associated Inc., 4104 148th Ave. NE, Redmond, WA 98052; G. Fox, British Columbia Ministry of Environment, Lands, and Parks, 777 Broughton St., Victoria, BC, Canada V8V 1X5; R. Zapf-Gilje, Golder Associates Ltd., 500-4260 Still Creek Dr., Burnaby, BC, Canada V5C 6C6; M. McFarlane, British Columbia Ministry of Environment, Lands, and Parks, 777 Broughton St., Victoria, BC, Canada V8V 1X5; and L. Swenson and B. Kelman, Golder Associated Inc., 4104 148th Ave. NE, Redmond, WA 98052
Comparisons of existing approaches to risk assessment allow better-informed development of new approaches. A detailed analysis of risk assessment methodologies developed by multiple countries (including other Canadian provinces, US national, several US states, Australia, New Zealand, the Netherlands, UK) was conducted at the request of Canadian regulatory agencies. Methodologies were classified into four categories: non-analytical, best professional judgement, US EPA-type, and enhanced US EPA-type. Both management and technical components were analyzed. A flexible risk assessment framework was developed for risk-based decision-making based on these methodologies that incorporated quantitative uncertainty analysis using probabilistic modeling and site-specific exposure factors when appropriate. Potential health risks to the residents of Wells, B.C. resulting from exposures to arsenic-containing mine tailings were evaluated as a case study application of the framework. Tailings produced from past gold mining and milling activities were disposed of in a lake and used as fill. Town soils with arsenic concentrations exceeding 150 mg/kg had been or were scheduled to be remediated. Incremental lifetime cancer risks attributable to remaining arsenic concentrations were evaluated, along with background risks attributable to naturally occurring arsenic. Hypothetical future-use scenarios involving utilization of tailings areas for residential and recreational use were also evaluated. Exposure pathways evaluated included ingestion of soil, dust, water and garden produce; inhalation of house dust and fugitive dust and dermal contact with soil, dust, and surface water. Uncertainty distributions were derived for exposure and toxicity factors using site-specific and literature information. Carcinogenic risks and systemic effects from arsenic exposures were evaluated using Monte Carlo simulations. Sensitivity analyses were performed to determine driving pathways and variables. Risks to the current population from arsenic exposures attributable to tailings were found to be negligible. Future-use scenarios involving more direct contact with tailings resulted in higher estimates of risk. The regulatory decision was to utilize the results of the probabilistic risk assessment in risk management. The driving exposure pathways involved direct contact with tailings; therefore, deed restrictions were implemented to prevent uncontrolled future development of tailings deposits. Use of site-specific exposure factors contributed to well-informed risk management.