Post‐environmental Impact Assessment Monitoring of Measures or Activities with Significant Transboundary Impact: An Assessment of Customary International Law

Abstract

Transboundary environmental impact assessment (EIA) is a rather new regulatory tool under international law. While there is consensus that customary international law obliges States to require transboundary EIA to be conducted for particularly invasive measures, the specific procedure and content of these assessment procedures is not stipulated by customary international law. It rather provides general principles that leave considerable room for interpretation by States when implementing transboundary EIA requirements and procedures. A procedural measure so far little discussed is post‐EIA monitoring of particularly invasive measures. Post‐assessment monitoring is, however, considered to be a necessary tool to enable stakeholders to manage environmental impacts effectively. Still, due to a lack of specific State practice and opinio iuris, an obligation to conduct or require post‐EIA monitoring does not exist as a separate provision of customary international law. Nonetheless, it may follow indirectly from the obligation to exchange information and the no‐harm rule.