Courtesy: VSI

Linn County Public Health Radon Study

Linn County Public Health (LCPH) conducted a radon evaluation project in 2013 to determine radon levels in new construction homes. LCPH obtained a list of building permits issued between 2008 and 2012 in unincorporated Linn County, Cedar Rapids, and Marion. A letter was sent to the addresses for participation. The evaluation project was under the supervision of staff who has received formalized training on radon mitigation and measurement. LCPH staff placed two short-term charcoal radon test kits on the lowest lived-in level of the home and according to testing instructions. Two kits were placed within four inches of each other as a quality control technique; the relative percent difference between the test kits was calculated to determine the validity of the kits and to quickly verify radon levels.

During the evaluation LCPH assessed the average radon levels, the type of radon system, and condition of the sump pit. The gravel base, vapor barrier, cracks and crevices in the concrete foundation were not assessed. All of these factors can influence radon levels within the home.

Evaluation Results

LCPH evaluated whether the homes had an active mitigation system, a passive system, or no radon reduction system (Figure 1). The visual assessment was conducted with the understanding that LCPH could only assess the conditions that existed at that time. Radon systems were assigned to one of the three following categories based on function:

1. Active Radon System: 3” or 4” PVC pipe that extends from below the building foundation to the exterior of the home with a powered vent fan actively pulling air below the foundation.

2. Passive Radon System: 3” or 4” PVC pipe that extends from below the building foundation to the exterior of the home, but which does not have a powered vent fan.

3. No Radon System: No evidence of a functional venting system to remove radon gas.

LCPH evaluated only what was visible in the basement or slab-on-grade and from the outside of the home, but did not observe the entire system or if the fan was operating. The determination of passive or active system was made on the observation of a pipe in the basement, a pipe coming out of the roof, and whether a manometer (present in active systems) was observed.

LCPH also assessed the condition of the sump pit. Radon enters your home through cracks and crevices, and unsealed sump pits provide a direct pathway for soil gases to enter the home and build up. Of the 97 homes with complete data, more than 50% had an unsealed sump pit. Homes with a sealed sump pit and no sump pit were considered functionally the same, and therefore lumped into one category (Figure 2).

Sealed Sump Pit: Described as no visible gaps, cracks, or crevices that will allow air flow from below the building foundation into the living environment. Gaps, cracks, and crevices are hermetically sealed with gaskets, silicone caulking, or equivalent.

Unsealed Sump Pit: Allows air to flow into the living environment from below the building foundation. An unsealed sump pit may be missing gaskets or a lid. May see PVC pipe terminate outside of the lid.

Of these data, LCPH compared the average radon levels by the type of radon system and sump pit. Of the 97 homes included in this evaluation, 96 were included in Figure 3. One home was excluded because radon screen levels were significantly higher (22.2 pCi/L) compared to other homes range of 0.3 to 13.2 pCi/L.

Summary of Figure 3

No Radon Removal System: 48% of homes without radon removal systems had average radon levels above the EPA action level of 4.0 pCi/L. However, average radon levels were slightly lower in homes with a sealed sump pit or no sump pit.

Passive Radon System: Homes with a passive radon system and either a sealed sump pit or no sump pit had lower average radon levels compared to those with unsealed sump pits. Average radon levels in homes with a passive radon system and an unsealed sump pit were near the EPA action level. However, 24% of homes with a passive radon system had radon levels above the EPA action level of 4.0 pCi/L.

Active Radon System: Homes with an active radon removal system and sealed sump pit had average radon levels closer to expected ambient air radon levels and none were above the EPA action level (4.00pCi/L).

Radon Evaluation Conclusions:

• Homes with an unsealed sump pit are more likely to have higher radon levels than homes with a sealed sump pit.

• Homes without a radon removal system are more likely to have higher radon levels than homes with a passive or active radon system.

• The majority of homes in Linn County do not have radon removal systems.

• More homes are likely to have an unsealed sump pit instead of a sealed or no sump pit.