City of Palo Alto
As a subconsultant to AECOM, Pathways completed a vulnerability assessment that considers both sea level rise and the response of the shallow groundwater layer to sea level rise. This low-lying city on the Bay edge is vulnerable to a wide range of flood risks and is currently a partner in the SAFER Bay program evaluating an alignment for a horizontal levee and/or other flood protections structures to protect the community from both coastal and riverine flooding. However, these structures may still leave wide areas of the city at risk to emergent groundwater flooding.
Pathways is working closely with the City of Palo Alto to identify the structures and areas of the city at greatest risk of potential groundwater flooding. Pathways first characterized the existing shallow groundwater surface, focusing on the wet winter conditions that occur after heavy rains when the groundwater table is at its highest elevation relative to the ground surface. This task relied on monitoring well data submitted to the Regional Water Quality Control Board and was augmented with geotechnical reports and soil borings that characterized both the depth to the water and the prevalent soil conditions. Once characterized and ground-truthed with City staff, future condition groundwater surfaces were developed for 6 sea level rise scenarios ranging from 12 to 84 inches.
Pathways identifyied areas of greatest risk and assessed the potential for contaminant plume migration and re-mobilization in active contaminated sites as the groundwater layer rises over time.