Leveraging Synergies: From Fragmented Development to Integrated Underground Planning

The subsurface represents a critical frontier for achieving sustainability goals, yet current development approaches remain largely uncoordinated and reactive. As societal challenges intensify —from climate change mitigation to urban densification— the underground is increasingly recognized as essential infrastructure space. However, the prevailing "first-come, first-served" or "last-resort" principles governing subsurface allocation result in fragmented management practices that overlook valuable synergistic opportunities between different underground uses. The question therefore arises how subsurface synergies can be strategically integrated into regulation and planning frameworks to promote sustainable, long-term underground development.

We identify three core principles that enable effective subsurface synergies: multifunctionality, circularity, and repurposing. Multifunctionality recognizes that underground spaces can serve multiple purposes simultaneously or sequentially, such as combining geothermal energy extraction with thermal energy storage, or integrating transport infrastructure with utility corridors. Circularity emphasizes cascading energy uses and resource efficiency, exemplified by utilizing waste heat from data centers for district heating networks or repurposing abandoned mines for energy storage. Repurposing extends the lifecycle of underground investments by adapting existing infrastructure to new functions, thereby reducing environmental impacts and optimizing resource utilization.

Through real-world case studies, we demonstrate how these principles can be operationalized within master planning and regulatory frameworks. These cases reveal both the opportunities for synergistic subsurface planning and the governance challenges that emerge from competing uses, jurisdictional fragmentation, and temporal mismatches between planning horizons and underground resource dynamics. Moreover, our analysis highlights critical barriers to achieving subsurface synergies: inadequate legal frameworks that fail to recognize three-dimensional property rights and long-term resource claims; sectoral silos separating energy, water, infrastructure, and environmental governance; insufficient data sharing and transparency about existing and planned underground uses; and lack of coordination mechanisms between stakeholders with different temporal perspectives and priorities. Overcoming these barriers requires moving beyond conflict resolution toward proactive synergy identification and facilitation.

We propose that effective subsurface governance must adopt a holistic, interdisciplinary, and integrated approach combining technical assessment with policy innovation. This includes developing spatial planning tools that visualize underground uses across multiple dimensions; establishing coordination platforms that bring together geoscientists, engineers, policymakers, and affected communities; creating legal mechanisms that recognize and incentivize synergistic developments; and implementing monitoring frameworks that track interactions between subsurface uses over time.

Our presentation contributes to the session's objectives by demonstrating how governance frameworks can either enable or constrain subsurface synergies, and by providing practical insights for researchers, policymakers, and practitioners seeking to leverage underground resources more sustainably. As pressure on subsurface space intensifies, the ability to identify, evaluate, and implement synergistic solutions becomes essential for ensuring that underground development serves both current and future societal needs while respecting environmental limits and intergenerational equity.