Discussion Forum

Hi,
I'm working on vapor intrusion modeling from subsurface into the overlying building. I have a large domain (100m X 100m) and a building (10m X 10m) with 2m basement is locating at center of the domain. There is a perimeter crack around the entire floor of the basement (the width is 0.1 m). Soil gas flow is defined based on Darcy's law. In Darcy's law module, the boundary conditions are no flow boundary imposed at the boundaries of the domain, lower horizontal domain boundary (groundwater table), and at all solid foundation boundaries except the crack. A pressure differential = -5 Pa is defined at the crack and the pressure at the surface considered to be atmospheric pressure. According to applied boundary conditions and with regard to mass conservation equation, the flow get into the domain from surface should be equal to flow out of the domain from the crack. But after running the model, I calculated surface integration of flow on the surface and in the crack; they were not equal. I searched a little bit and I figured out that for these cases weak constraints should be considered in order to get accurate mass balance. I'm trying to add weak constraints but I don't know which boundaries I should include and what constraint expression I should add. Does anyone know how should I do this? I can also upload the model here. It may make more sense. If anyone can help me, I will be really thankful.