Examining the role of sub-foundation soil texture in chlorinated vapor intrusion from groundwater sources with a two-layer numerical model.

In this study we investigate the role of the sub-foundation soil texture in determining groundwater source-to-indoor air attenuation factors. A three-dimensional numerical model was used to simulate a series of two-layer scenarios, involving different sub-foundation and deep soil textures, foundation types and groundwater source depths. The results indicate that if the sub-foundation soil permeability is larger than 10-11  m2 , the convection dominates the soil gas transport into the building, and the indoor air concentration increases by half an order of magnitude with one order of magnitude increase of the sub-foundation soil permeability. Otherwise, diffusion plays a more important role and the sub-foundation soil texture does not cause significant variation of indoor air concentration. We found that, independently from the deep soil texture, the capillary fringe offers the main resistance to vapor transport. In these cases, the deep soil texture could induce at most half an order of magnitude of variation in total effective diffusion coefficient in deep soil as well as groundwater source-to-indoor air attenuation factors. Finally, we found that, as the thin capillary zone represents the higher resistance to upward soil gas flow, groundwater source depth has little influence in determining the chlorinated vapor intrusion risk.