Sub-slab soil gas sampling helps evaluate the potential impact of vapor encroachment on indoor air quality. Vapor intrusion occurs when volatile contaminants migrate from the subsurface into buildings through cracks or openings in foundations. By sampling the soil gas beneath the building’s foundation, it becomes possible to identify the presence of hazardous vapors and determine if they are entering the building. By analyzing the composition and concentration of volatile organic compounds (VOCs) in the soil gas, environmental professionals can identify specific contaminants and their potential sources. This knowledge is crucial for implementing effective remediation strategies and preventing further vapor encroachment.