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Ecological Risk Assessment

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CN conducted an ecological risk assessment for the site to evaluate the potential risk from the derailment and crude oil release to present ecological receptors including birds, mammals, fish, and other terrestrial and aquatic life. The risk assessment used laboratory results from sediment, benthic macroinvertebrates (organisms living at the sediment/water boundary), and surface water samples to assess risk to these receptors.   

The samples were used to support a Preliminary Ecological Risk Assessment (ERA), which covered the Makami River from upstream of the derailment site, to the railway trestle bridge located southeast of Gogama. The resulting data were first compared to Ontario's conservative ecological screening levels for surface water and sediment, as part of the Preliminary ERA, to determine which oil components would need further evaluation in the Comprehensive ERA and which areas may require active remediation (i.e. sediment removal). The results of the Preliminary Ecological Risk Assessment were submitted to the regulatory agencies for review. 

A Comprehensive ERA was completed in areas where oil components exceeded existing screening levels in the Preliminary ERA. A baseline ecological risk assessment (BERA) was prepared as part of the Comprehensive ERA which incorporated parameters, specific to both the oil components (e.g., uptake and accumulation in organisms, refined toxicity levels) and to the site (e.g., species present, feeding ranges, food web, habitat quality), that helped refine the screening levels, define the remedial area, and provided a more realistic risk statement for the area. 

Based on the results of the Comprehensive ERA, it was concluded that there was potential risk to ecological receptors in the portion of the Makami River where the derailment occurred (from just upstream of the rail bridge to just downstream of the Bailey bridge) due to elevated concentrations of polycyclic aromatic hydrocarbons (PAHs).  This area was defined as the remedial area. It was also determined that there was very low risk to ecological receptors outside of the remedial area. As such, CN began planning to remove the impacted sediment from the area identified in the Comprehensive ERA.

Learn more about our sediment remediation activities.