Properties where soil and/or groundwater have been affected by chemical releases, the potential exists for vapors to emanate from affected soils and/or groundwater and negatively affect air quality inside an overlying enclosed building. Vapors can permeate through the concrete foundation and enter enclosed buildings through sewer lines, cracks in the foundation, or utility penetrations in the building foundation.
About Vapor Intrusions
If soil or groundwater samples are detected at concentrations above state cleanup levels, there is a chance a vapor intrusion condition could exist inside an overlying building. The EPA uses an attenuation rate of 0.03 for estimating indoor air concentrations resulting from affected soils and/or groundwater beneath a building slab. The EPA also offers a Vapor Intrusion Screening Level (VISL) calculator that estimates indoor air concentrations based on soil-gas or sub-slab vapor results.
Indoor air sampling will eventually confirm whether a vapor intrusion condition exists; however indoor air sampling is only recommended when chemical concentrations in soil and/or groundwater indicate a vapor intrusion condition could exist. Common cleaning chemicals used in normal business operations tend to emit vapors that could be detected in indoor air samples and could be falsely interpreted as a vapor intrusion concern
Factors such as building airtightness and HVAC efficiency can significantly reduce the potential for a vapor intrusion condition to exist.
Soil-gas samples are collected outside buildings. Samples are collected by advancing soil borings and installing implants or small diameter wells that will allow for collection of soil-gas samples. Soil gas sample results can then be evaluated by applying a 0.03 attenuation rate and by using the EPA VISL calculator to estimate chemical concentrations that could be present in indoor air based on conservative default values.
Sub-slab samples are collected inside buildings. Sub-slab samples are collected by drilling a hole through the concrete slab and installing a vapor pin® to allow for collection of soil-gas samples beneath the building foundation slab. Soil gas sample results can then be evaluated by applying a 0.03 attenuation rate and by using the EPA VISL calculator to estimate chemical concentrations that could be present in indoor air based on conservative default values.
Samples are collected inside buildings. Samples are collected directly from indoor air over an extended time, usually 8 hours to 24 hours, depending on property use (industrial/commercial vs residential).
Items such as cleaning supplies, new paint, new carpets, and construction activities could contribute to indoor air quality background levels, thus indoor air sampling is only recommended when soil, groundwater, or soil-gas conditions indicate a vapor intrusion condition could exist and should be conducted in coordination with sub-slab vapor samples.