Abstract:

The generation, mobilization, and attenuation of acid rock drainage and metal leaching (ARD/ML) is a complex process governed by physical and chemical processes. Effective mitigation and risk management requires a robust conceptual model and characterization of contaminant sources, hydrology and hydrogeology. This study presents the site investigation and geochemical evaluation undertaken for the remote abandoned Atlin Ruffner Mine, which operated between 1900 and 1981.

Mining operations generated mine waste that caused ARD/ML and the contamination of soil, surface water and groundwater. Investigations were conducted at eleven Areas of Potential Environmental Concern. Samples of waste rock, soil, sediment, groundwater and surface water were collected to characterize geochemistry, contaminant sources, and attenuation processes. A water balance and water quality model was developed to quantify the impact of each source on the receiving environment.

Geochemical testing found that most waste rock was potentially acid generating. Disturbed soils in proximity to adits and waste rock piles also exhibited metal contamination. Metal concentrations in undisturbed soils were similar or greater than found in disturbed soils and mine waste, and contributed significant contaminant loads to the receiving environment. Surface water quality results found that some metals precipitate out of solution as source waters discharging from the underground mine equilibrated with the atmosphere along the surface water flow pathway, and mitigated impacts to the receiving environment. These findings provide useful information for risk assessment and mitigation measures to protect human health and the environment.

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Michael Sanborn