Sea level rise, groundwater rise, and contaminated sites in the San Francisco Bay Area, and Superfund Sites in the contiguous United States

Rising sea levels (SLR) will cause coastal groundwater to rise in many
coastal urban environments. Inundation of contaminated soils by
groundwater rise (GWR) will alter the physical, biological, and
geochemical conditions that influence the fate and transport of existing
contaminants. These transformed products can be more toxic and/or more
mobile under future conditions driven by SLR and GWR. We reviewed the
vulnerability of contaminated sites to GWR in a US national database and
in a case comparison with the San Francisco Bay region to estimate the
risk of rising groundwater to human and ecosystem health. The results show
that 326 sites in the US Superfund program may be vulnerable to changes in
groundwater depth or flow direction as a result of SLR, representing 18.1
million hectares of contaminated land. In the San Francisco Bay Area, we
found that GWR is predicted to impact twice as much coastal land area as
inundation from SLR alone, and 5,297 state-managed sites of contamination
may be vulnerable to inundation from GWR in a 1-meter SLR scenario.
Increases of only a few centimeters of elevation can mobilize soil
contaminants, alter flow directions in a heterogeneous urban environment
with underground pipes and utility trenches, and result in new exposure
pathways. Pumping for flood protection will elevate the salt water
interface, changing groundwater salinity and mobilizing metals in soil.
Socially vulnerable communities are more exposed to this risk at both the
national scale and in a regional comparison with the San Francisco Bay
Area.