Vapor Intrusion

Engineering Solutions to Vapor Intrusion at Brownfield Sites:

Using case-studies of two Brownfield sites in New Jersey, ENVIRON will present in detail two different design approaches for vapor mitigation systems (VMS): sub-slab depressurization and sub-slab ventilation. The most effective design approach depends on site-specific conditions, applicable regulatory framework and applicable technical guidance. Specifically, USEPA and various state agencies such as MADEP, PADEP, NYSDEC and most recently NJDEP, have developed vapor intrusion guidance documents. Although there are many similarities in the guidance documents, the differences can be considerable. Therefore, this presentation will provide a comparison of the primary differences in the documents including an analysis of the different critical chemical of concern screening criteria, matrix specific screening approaches, soil gas sampling, and indoor air sampling techniques. As an example, one guidance document allows the use of Johnson & Ettinger (J&E) model to conservatively estimate vapor intrusion potential based on site-specific ground water and/or soil gas data and critical building parameters. However, there are subtle but noteworthy differences in the J&E model default input parameters prescribed by the various regulatory agencies, which can result in a significant variation in modeled indoor air concentrations and consequently the selection of the appropriate VMS design approach. In addition, several of the most critical J&E model input parameters (such as Qsoil, pressure differential, soil characteristics, etc.) are highly sensitive and dramatically affect the VMS design. Common pitfalls to avoid when using agency-mandated input parameters will also be presented. Using the two New Jersey case studies as examples, a decision flowchart for selecting the appropriate VMS design (passive, active sub slab depressurization or ventilation