Formatted Title
The Challenge of Mitigating the Risk of Vapor Intrusion in Residential Areas
Background/Objectives
In a deactivated industrial unit, the environmental investigation conducted in the external area, in neighboring residences, confirmed the vapor intrusion in the following lines of evidence: Substances of interest concentrations above the reference value in the ambient air samples collected inside the residence, in the drains and conduits identified using a portable GC/PID chromatograph, as well as concentrations in the samples collected in the sub slab wells in the external area of the residence. Based on this evidence, the conceptual model of intrusive vapors identified a potential risk in the intrusion routes related to the preferential flow of drains and conduits, which constitute a potential preferential path between the subsoil and the closed environment.
Approach/Activities
The action in the area was designed to isolate the concentrations by preventing preferential paths through emergency engineering measures and risk mitigation with the implementation of an active sub slab depressurization system (SSD). The SSD system included the installation of vapor extraction points in the sub slab and underground to generate a vacuum and extract any concentrations available in the environment. The measures described were designed to maintain the structures and reduce the impact on people and were defined in a way that was not invasive and in harmony with the occupation of the properties. In addition to the engineering measures, communication actions were carried out with stakeholders (residents, environmental agency, client, health surveillance).
Results/Lessons Learned
The emergency actions were implemented in a short period of time and in harmony with the use and occupation of the areas, with the purpose of reducing the impact on residents and acting on the risks identified. The system in operation and its monitoring have made it possible to identify the vacuum and have reduced concentrations by up to 99% compared to the baseline concentrations detected in both the sub slab and the subsoil. The system is currently in operation and further investigations are being carried out to map sources and take remediation action.