First let’s review a few basic radon entry and behavior basics before we begin thissection.
Remember, the mechanics of radon entry into a home or building first require that a source of radon be present near the foundation. The 3 primary sources of radon are:
Soil or Bedrock
Well Water or Aquifer
If a source for radon is present, a pathway from the source to the home or building must be present for the radon to “get to” the home. Some common pathways are:
Gravel or pebbles
Cracks in soil
Cracks, fissures, Caverns in rock
Perforated pipe (as used in drainage systems)
Openings in foundation
Finally, if there is a radon source and a pathway by which the radon can get to the house or building, there must be a transport mechanism, or a “force” drawing in the radon gas. The 4 Transport Mechanisms of Radon (a force drawing radon into the building) are:
Concentration Gradient Diffusion
Pressure Driven Airflow
You may recall that Pressure Driven Airflow is the predominant transport mechanism that brings radon from the soil into the air of a home or building. As the illustration below indicates, well water, emanation and diffusion are secondary culprits of radon entry. Soil to air transport accounts for 85-90% of radon entry.
What causes Pressure Driven Airflow?
Natural convective currents and Stack effect
Why is this topic important to review?
Queries from Realtors and consumers regarding why “temporary” or “secondary” mitigation efforts (i.e. sealing sump pit, foundation cracks, etc.).
Queries regarding levels that have changed over time (i.e. the source may have moved as the earth moved/settled over time).
Queries regarding why one home has a problem and not the house next door.
Queries regarding radon result changes from one owner to another (i.e. Pressure driven airflow due to difference in occupant usage).
Understanding these principles will help the radon professional to better understand that radon levels are determined by entry mechanisms, behavior of the home/building, the occupants, the activity inside the home/building and a multitude of other factors including weather and environmental factors culminate to determine radon levels. Radon, and the process of testing and mitigating is a science. There is not a blanket assumption (a common mistake made by radon professionals) that can be made to the consumer regarding “why” radon is present or “how” it can be mitigated without performing the scientific process of testing.