Formatted Title
Through the Looking Glass: Revamping the Vapor Intrusion Conceptual Site Model in Response to Climate Change
Background/Objectives
Climate change poses unique challenges for vapor intrusion (VI) sites, particularly those in coastal areas. Sea-level rise (SLR) and extreme weather conditions are predicted to increase groundwater table elevations along U.S. coastlines over the coming decades. A prolonged rise in the groundwater table can potentially mobilize previously sequestered vadose zone contaminants or cause groundwater plumes to enter shallow utility conduits, including sewer systems, which could increase potential VI risks. Rising groundwater tables and changes to soil moisture could also reduce the effectiveness of VI mitigation methods like sub-slab depressurization. Alternatively, a rising groundwater table could decrease VI risk by submerging subsurface sources. Currently, the potential impacts of a rising groundwater table on VI remain largely conceptual and based on long-term projections.
Approach/Activities
A desktop study supported by reduced order modeling was used in the initial assessment of climate change-related hazards on the VI conceptual site model (CSM). MODFLOW-USG-Transport (USGT) was used to simulate SLR projection scenarios, including the impact of groundwater table rise on the migration of vadose zone sources. Finally, a desktop study of publicly available contaminated site data was conducted to gain a better understanding of baseline conditions and current impacts at select sites.
Results/Lessons Learned
Preliminary assessment indicates groundwater inundation and groundwater emergence, driven by climate change and SLR, are likely the primary climate-related hazards for coastal VI sites. Simulation results show that groundwater will predominately flow horizontally from upgradient areas following a rise in groundwater table elevation over 50 and 100 years, suggesting negligible vertical transport of contaminants during a period of sustained groundwater table rise. However, transient effects that can cause groundwater table oscillations, including episodic recharge, have yet to be considered. Initial results of the desktop study indicate limited data availability for sites with sustained increases in groundwater table elevation, but inland regions where groundwater pumping has recently decreased need to be further evaluated. Overall, the results highlight data gaps for VI sites with prolonged groundwater table rise, emphasizing a need for a structured framework to address potential changes to VI risks due to climate change. Recommendations for an initial assessment framework will be provided.