Vapor intrusion occurs when there is a migration of vapor-forming chemicals from subsurface sources into nearby buildings. Vapor intrusion is a potential concern at any building, existing or planned, located near soil or groundwater contaminated with toxic chemicals that can volatilize. Building types and conditions are also important factors in assessing the potential for subsurface vapor intrusion. A variety of meteorological conditions, such as temperature, barometric pressure, wind, rainfall, and snow cover, can influence soil gas concentrations and vapor flux into a building. Vapor intrusion mitigation methods all rely on the conceptual model of a vapor migration mechanism. Vapor flows from a high-pressure regime to a low-pressure regime when there is a gradient. Sub-Slab Venting system functions by creating a pathway to vent sub-slab vapors outside through pipes and stacks and/or drawing in air from outside to dilute the undesired volatile compounds in sub-slab air.