Social ecological system framework as a decision-making tool for risk mitigation: A superfund site case study

Several studies have reported vapor intrusion (VI) occurring when volatile organic compound (VOC) vapors are transported through subsurface piping systems into building spaces (e.g. conduit VI). Site-specific risk assessment and risk management practices are complicated and evolving for conduit VI, especially at large hazardous waste sites, like Superfund sites, where many stakeholders are involved and have varied interests. Here, we propose a social ecological system (SES) framework as a decision-making tool to inform risk mitigation decisions. We demonstrate the SES framework using field data associated with a Superfund site near San Francisco, California. We evaluate sewer invert elevation and groundwater elevation data, as well as pre- and post- mitigation VOC concentration data within a sewer system. Unexpectedly, the sewer located above the groundwater table was determined to be a potential source of conduit VI risks. The SES framework describes how typical stakeholders associated with the site can affect and be affected by mitigation activities. It informs decisions about mitigation implementation and long-term operation efficacy by considering stakeholder roles and interests. Ultimately, gas siphons were selected as the mitigation technology for the example site. To date, approximately 6 gas siphons have been installed to mitigate conduit VI risks throughout the community. Collectively, our findings advance risk management decisions and highlight key considerations for risk mitigation approaches at hazardous waste sites, including Superfund sites, especially where VI risks are a concern.