Sea-level and groundwater rise increase the potential for indoor exposure to volatile organic compounds near contaminated sites

Sea-level rise threatens cities with frequent flooding and a rise in unconfined groundwater elevations. Groundwater will emerge at the surface in low-lying areas and a wide range of hidden impacts could occur in urbanized areas where the vadose zone is shrinking. Rising groundwater can mobilize soil contaminants, increase sewer infiltration, and increase the need for dewatering by pumping. Nationally, tens of thousands of coastal sites with contaminated soil managed by government agencies may be exposed to unexpected contaminant mobilization. This study developed a method that can assess the potential for volatile organic compounds (VOCs) to be mobilized in soil and enter indoor air via sanitary sewers. Previous approaches examined flow directions of plumes and considered dispersal of VOCs in sewers but have not assessed potential impacts of rising groundwater. Our method focuses on risks to the use of buildings with particularly vulnerable occupants (schools, daycares, and residential buildings). As a case comparison, we investigated 21 urban sites that were selected from more than 1,800 in the San Francisco Bay Area with VOC contamination, shallow and rising groundwater, and moderate to high classifications of social vulnerability. The screening tool showed 22 schools or daycares and 1,264 residential structures represented 54% of all structures where sanitary sewer connections are plausible pathways for VOC intrusion indoors with sea-level rise. These results indicate potentially new VOC pathways of exposure with changing groundwater conditions. The impact of groundwater dynamics and rising seas on future VOC mobilization should be assessed at the tens of thousands of VOC-contaminated sites in the US and countless sites globally.