| Abstract: | Many vapor intrusion (VI) mitigation systems involve some form of gas extraction from below the concrete floor slab of a building to create a static vacuum below the slab that meets or exceeds a value specified in a guidance document or standard. This also results in some degree of ventilation below the floor slab, which reduces vapor concentrations and achieves some level of mass removal of target chemicals. The relative contribution of vacuum and ventilation to protecting building occupants is generally not quantified. Recent research completed under ESTCP Project ER-201322 yields some new insights using new lines of evidence. The results warrant changes in the guidance documents and standards of practice to promote and enable VI mitigation system designs that vary according to the transmissivity of the material below the floor slab and the rate of vertical leakance of indoor air across the floor slab and incorporate additional lines of evidence including the mass removal rate. |
