Radon Abatement

1. Identification: Radon Testing

Radon is invisible and odorless, so its presence is confirmed only through testing. The process must accurately measure the concentration of Radon-222 (Rn−222) decay over a specific time period.

• Action Level: The U.S. Environmental Protection Agency (EPA) recommends mitigation when the indoor air concentration is 4.0 pCi/L (picoCuries per liter) or higher.

• Test Types:

  • Short-Term Tests (2-90 days): These use activated charcoal canisters or alpha track detectors. They provide a quick snapshot but can be affected by weather and seasonal variations.

  • Long-Term Tests (over 90 days): These use alpha track detection and provide a more accurate measure of the home's year-round average radon level, which is the most relevant indicator of long-term health risk.

  • Continuous Radon Monitors (CRMs): Electronic devices used by professionals that continuously measure and log radon levels, providing hourly data for detailed analysis.

2. Abatement Method: Sub-Slab Depressurization (SSD)

The most effective and common method of radon abatement is Sub-Slab Depressurization (SSD). This technique addresses the pressure differential that draws radon into the home by reversing the flow direction.

The Scientific Principle: Pressure Reversal

SSD works by creating a negative pressure field beneath the foundation slab that is lower than the pressure inside the house. This counteracts the normal stack effect, ensuring that soil gas is sucked out and vented before it can enter the living space.

Key Steps of SSD:

1. Suction Point Creation: A hole (suction pit) is drilled through the concrete slab into the underlying gravel or soil (the communication zone). The surrounding material is often excavated to maximize the zone of influence.

2. Piping Installation: A pipe (typically 3- or 4-inch diameter PVC) is inserted into the hole and sealed tightly into the slab using a non-shrink grout or polyurethane caulk.

3. Ventilation Routing: The piping system runs vertically, usually through an unconditioned space (garage, closet, or outside) up to the attic.

4. Exhaust: The pipe is vented through the roof, ensuring the radon-laden air is released far enough above the building to safely dissipate into the atmosphere, preventing re-entry.

3. Equipment Used in Radon Abatement

Specialized equipment is necessary to establish and maintain the required negative pressure.

A. Radon Fan (In-Line Centrifugal Fan)

This is the heart of the SSD system.

• Function: It is a continuously operating, high-performance in-line centrifugal fan installed on the vertical suction pipe, usually in the attic or exterior of the building.

• Placement: It must be installed in an unconditioned space (attic, exterior) to ensure that if the fan housing develops a leak, radon is not dumped directly into the living space.

• Specifications: Fans are selected based on the size of the house, the permeability of the soil, and the total distance (suction field) they must depressurize. They are designed for continuous, quiet operation and low energy consumption.

B. Monitoring and Safety Equipment

• U-Tube Manometer: A simple, yet essential, liquid-filled U-shaped gauge installed on the suction pipe, typically in a visible area (like a basement wall). It visually indicates the pressure differential. If the liquid levels are unequal, the fan is operating and creating suction. If they are equal, the fan has failed, or the system is blocked.

• Air Permeability Sealants: High-grade, durable polyurethane or silicone sealants and hydraulic cement are used to airtightly seal all cracks, penetrations, and perimeter joints in the foundation floor. This directs the fan's suction effort to the sub-slab area rather than wasting it on pulling air through cracks in the floor.

• Vapor Barrier/Soil Gas Retarder: In crawlspaces, a thick polyethylene sheet (6-mil or greater) is installed over the dirt floor and sealed to the foundation walls. A pipe is inserted beneath this barrier, and the fan is used to create suction beneath the plastic, a process called Sub-Membrane Depressurization.