Areas where buildings are not currently present require evaluation for the VIAP because reasonable future uses must be considered. Additional consideration for future uses is needed when the vapor source is located less than ten (10) feet below the ground surface because a representative soil gas sample can be collected; however, it may not represent or evaluate all potential future uses (e.g. residential home with a basement). Whether or not an unacceptable risk from the VIAP will occur in a future building requires an understanding of the vapor source, how the future buildings could be constructed, and what the future exposure scenario could be (e.g. VI or direct volatilization). Modeling done by USEPA (2012 and 2013) provides simplified simulation models to illustrate graphically how subsurface conditions with a significant vapor source concentrations and surface characteristics, such as the presence or absence of a building, may impact the concentrations detected.
If a future change in land use could result in an exposure scenario that was not or cannot be evaluated, then there will be a need to place a land or use restriction on the property to ensure that the exposure scenario that was evaluated remains the same. If there is no building present and all reasonably anticipated future uses can be evaluated with appropriately placed soil gas samples, then land or use restrictions would not be required even with soil or groundwater concentrations above criteria or screening levels. Soil gas sampling allows for a determination that the vapor source does not pose an unacceptable vapor intrusion risk for any use. In addition, per Rule 299.14(5) and Rule 299.24(5) soil gas sampling data can be used to show compliance with the soil and groundwater VIAC, so the soil gas data can show that the soil and groundwater is not a vapor source. Further information on when a land or resource use restriction is required, and other site management strategies is described in Section 6 and Attachment D, Response activities are further detailed in Volume 5 – Response Activity.