What is soil vapor intrusion?
The phrase “soil vapor intrusion” refers to the process by which volatile chemicals move from beneath the ground into the indoor air of overlying buildings. Soil vapor, or soil gas, is the air found in the spaces between soil particles. Because the air pressure inside may be lower than in the soil, this vapor may enter buildings through cracks in slabs or basement floors and walls, and through openings around sump pumps or where pipes and electrical wires go through the foundation. Heating, ventilation or air-conditioning systems may reduce the air pressure inside, drawing soil vapor into buildings. Chemicals that readily evaporate or vaporize are called “volatile chemicals.” Volatile chemicals include volatile organic compounds (VOCs). Subsurface sources of volatile chemicals may include contaminated soil and groundwater, broken pipes, or buried wastes. If soil vapor is contaminated and enters a building as described above, the air quality inside the building may be affected. When con
