One Pipeline and Two Impact Assessments: Coproduction, Legal Pluralism, and the Trans Mountain Expansion Project.

Canada's Trans Mountain Expansion Pipeline project is one of the country's most controversial in recent history. At the heart of the controversy lie questions about how to conduct impact assessments (IAs) of oil spills in marine and coastal ecosystems. This paper offers an analysis of two such IAs: one carried out by Canada through its National Energy Board and the other by Tsleil-Waututh Nation, whose unceded ancestral territory encompasses the last twenty-eight kilometers of the project's terminus in the Burrard Inlet, British Columbia. The comparison is informed by a science and technology studies approach to coproduction, displaying the close relationship between IA law and applied scientific practice on both sides of the dispute. By attending to differing perspectives on concepts central to IA such as significance and mitigation , this case study illustrates how coproduction supports legal pluralism's attention to diverse forms of world making inherent in IA. We close by reflecting on how such attention is relevant to Canada's ongoing commitments, including those under the UN Declaration on the Rights of Indigenous Peoples.