The vadose zone, defined as the geologic media spanning from the land surface to the groundwater table of the first confined aquifer, plays a critical role within the biosphere. Understanding fluid transport processes, including both water and gas flow and transport, in the vadose zone is essential for protecting groundwater resources, human health, infrastructure, and the environment.

Due to intrinsic multiphase characteristics in the vadose zone, interactions with atmosphere and aquifers, and inherent spatial heterogeneity of the soil properties, there are many challenges in fundamental theories and techniques regarding sampling and modeling fluids flow and transport in the vadose zone. Additional challenges are found in designing remediating and engineering applications, such as vapor intrusion and mitigation, hydrocarbon contamination and remediation, contaminant infiltration with rainfall, and energy and water exchange with the atmosphere.

This Special Issue focuses on various areas of natural soil water and gases produced by environmental contaminants below ground, including, but not limited to: fundamental, experimental, numerical, and analytical studies of how physical, chemical, biological, and climatic processes interact to control dynamic processes of fluid flow and transport in the vadose zone; and emerging technologies for in situ monitoring and predictions of the spatial and temporal distribution of fluid and vapor concentrations as well as for mitigating deleterious gases in the field. Contributions are solicited from hydrologists, geophysicists, soil physicists, agricultural scientists, climatologists, microbiologists, ecologists, biogeochemists, and others working on theoretical, mathematical, experimental, and technological aspects related to vadose zone fluid transport in natural and managed ecosystems, with application to water resources, remediation, agriculture, urban hydrology, climate, and infrastructure engineering.

Potential topics include but are not limited to the following:

• Natural soil water and gases
• Vapor intrusion and mitigation
• Water and energy exchange in the vadose zone
• Experimental (laboratory and field) investigation of the vadose zone
• Numerical modeling of fluid flow and transport
• Analytical investigation
• Emerging technologies for in situ monitoring
• Emerging technologies for predictions
• Emerging technologies for mitigating deleterious gases
• Remediation of the vadose zone