Soil Vapor Intrusion

Soil vapor intrusion occurs when chemicals move from an underground source into the indoor air of buildings. This is also how radon gas enters into buildings. Soil vapor is the air in between soil particles. It can 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. Soil vapor can become contaminated when chemicals evaporate from underground sources. This contaminated soil vapor can then affect indoor air quality if it enters buildings.

Chemicals Associated with Soil Vapor Intrusion

Chemicals that evaporate and contaminate soil vapor are most frequently volatile organic compounds (VOCs) from:

  • Solvents used for dry cleaning that were spilled
  • Improper disposal of solvents used in manufacturing
  • Leaking underground tanks
  • Chemical or oil spills

Volatile Chemicals in Commonly Used Products

Chemicals in products we use every day in the home can also impact indoor air. These can come from:

  • Paints, stains, and finishes
  • Cleaners and room deodorizers
  • New furniture, carpets, and wood floors

Addressing Soil Vapor Contamination

Investigating soil vapor intrusion typically requires collecting soil vapor, sub-slab vapor, indoor air, and outdoor air samples. Based on the sampling results, next steps may include:

  • No further action. No additional actions are recommended to prevent or address human exposures.
  • Additional sampling. Additional sampling may be performed to determine the extent of soil vapor contamination and to verify questionable results.
  • Monitoring. Monitoring (sampling on a recurring basis) is typically conducted if there is a significant potential for soil vapor intrusion to occur should building conditions change.
  • Mitigation. Mitigation may include things like sealing cracks in the building's foundation, adjusting the building's heating, ventilation and air-conditioning system to maintain a positive pressure to prevent infiltration of subsurface vapors, or installing a sub-slab depressurization system beneath the building.

Find guidance on how to conduct a soil vapor intrusion investigation.

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