Radon gas is carried by the soil gas under the home into the lowest level of the home. Radon exists in the soil gas if its immediate radioactive parent, Radium, is present in the formation under the home. Radium, in turn, comes originally from the radioactive decay of Uranium in the geological formation.
Eliminating the incursion of Radon into the home involves several steps.
- Openings in the foundation and the floor need to be sealed. French drains, cracks, utility openings, open sumps, need to be closed as much as possible.
- The “driving force” that pushes the soil gas into the home must be reduced.
- The concentration of Radon in the soil gas must be reduced.
Step #1 is straightforward. All possible leakage paths must be closed or reduced.
Steps #2 and #3 are coupled. One or more holes are drilled through the floor into the sub-slab space, and a fan is installed to pump away some of the soil bgas, venting it to the open air above the roof-line. This pump does two things: it lowers the ambient soil gas pressure, lowering the “driving-force” and it replaces the Radon-loaded soil gas with cleaner make-up air.
The job of the Mitigation system designer is to evaluate the porous condition of the fill under the slab, using sensitive micro-manometers, to determine the location of the slab penetration(s) and the size of the fan itself. This is a critical service by a skilled system designer to plan an efficient system and to control the cost to the homeowner.
Radon concentration is measured in units called
“picocuries of Radon per liter of room air.”
Abbreviated “pCi/l”
State and federal agencies, including the EPA, the U.S Surgeon General, and the Centers for Disease Control & Prevention have recommended that if the measured Radon concentration exceeds 4.0 pCi/l, Radon mitigation should be considered.
FAQ:
Can Radon come from materials actually used in the building construction as well as from geological sources beneath the structure?
Answer:
Yes, but rarely. The only place we’ve found Radon to originate from building materials is in Florida, where Phosphate mill tailings have been used in concrete. High levels of Radon in a 9th floor condo apartment was reported to us, and there is no clear source other than in the concrete used in the building’s construction. In a case such as this a normal mitigation system is useless, and an air-exchange approach is the only solution.