EVALUATION OF INDOOR AIR QUALITY

Migration of Contaminants

The drawing on the right illustrates how a contaminant source  (industrial area in this case) may result in groundwater contamination beneath the facility.   Groundwater flow then transports contaminants downgradient where they may impact other properties.    If any of the contaminants in the groundwater are volatile, they may rise through the overlying unsaturated soils and enter indoor air.   The level of the building that is impacted first by contaminants from the subsurface, is the lowest level.   In buildings with a basement, the basement air is usually impacted first and by the highest concentrations of  contaminants.  

Sampling

Samples may be collected on the site with a portable analyzer, or collected in containers for either laboratory analysis or analysis in a field laboratory.   Tubes with absorbent material may also be used to collect gas samples over a measured period of time.   The samples should be collected to reflect the air volume that is being evaluated (e.g. in a room at breathing level).   Enough samples should be collected to evaluate patterns of contaminant entry and migration within the building.   Containers may include Tedlar® bags, a material resistant gas permeation and Summa canisters, containers constructed of stainless steel.   Samples can be "grab samples" or air samples collected over a measured period of time.   Sometimes soil gas samples are collected from beneath or adjacent to a building to evaluate the gas concentrations in the subsurface that have not been affected by activities or substances that are in the building.   Buildings commonly contain numerous volatile substances including:

• The presence of volatile substances that may be used or stored in the building (e.g. paint, solvents, and cleaning agents).
• The building may be heated by a system that burns hydrocarbons (e.g. fuel oil or natural gas). Volatile hydrocarbons may be present in indoor air from the heating system, storage, or transmission lines.

Analysis

Analyses that are conducted depend on the objective of the evaluation.   Analytical methods may be those of regulatory agencies (e.g. U.S. EPA or State regulatory agencies).   We have found that a screening assessment of the impact on indoor air can be made using the Johnson and Ettinger Model on the U.S. EPA website. 

Some Useful Links

Following are some hyperlinks that can further assist with the evaluation of indoor air quality:

• U.S. EPA website, Indoor Air Quality page.
• Johnson and Ettinger Model for screening impact of sub-slab air concentrations on indoor air concentrations on the U.S. EPA website
• State of New York (USA) Guidance for Evaluating Soil Vapor Intrusion.
• Breeze Air Dispersion Modeling Software