Carbon footprint in contaminated-site remediation: a systematic review of accounting methodologies, influencing factors, and decarbonization strategies

The remediation of contaminated sites is essential for environmental protection but often carries a substantial carbon footprint due to energy‑intensive processes, material consumption, and transportation logistics. This review systematically synthesizes current knowledge on carbon-footprint management in contaminated-site remediation, focusing on accounting methodologies, comparative technology assessment, key influencing factors, and decarbonization strategies. Four accounting approaches are critically evaluated, namely life cycle assessment (LCA), input-output analysis, intergovernmental panel on climate change calculation, and hybrid LCA, and their applications across site‑specific, regional, and macro scales are examined. A comparative analysis reveals a conditional carbon-footprint hierarchy: nature‑based solutions < optimized in situ physical and chemical treatments < energy‑intensive thermal and ex situ methods. However, reported footprints vary widely even within the same technology due to differences in contaminant type, site geology, treatment intensity, local energy mix, and regulatory context. Emerging decarbonization strategies such as precision remediation, on‑site renewable energy, biochar‑based amendments, green logistics, and decision‑support tools are evaluated in terms of their evidence base, implementation constraints, and associated trade‑offs. Coupling multiple decarbonization strategies can yield synergistic benefits; however, project‑specific LCA is essential for robust evaluation. Additionally, key methodological challenges, including emission-scope coverage, embodied-carbon accounting, temporal-boundary definition, and uncertainty reporting are identified as barriers to cross‑study comparability. This review provides a critical, evidence‑based foundation for researchers, practitioners, and policymakers to align contaminated-site remediation with global carbon-neutrality goals.