A sump pit is a hole in your basement floor that opens straight onto the soil and drain tile under the house. Left open, it is an easy way in for radon: CDC’s toxic substances agency lists sump holes alongside foundation cracks and dirt crawlspace floors as the main entry points (ATSDR). A radon sump cover is an airtight lid that closes that opening while letting the pump keep working.
A cover alone or as part of a system?
As part of a mitigation system. This is where sump covers do the most good. In sump-hole suction, the sump is capped so it still drains water and doubles as the suction point for the radon pipe (EPA, Consumer’s Guide to Radon Reduction). In drain-tile suction, the pipe connects to the drain tile and covers go on the sump baskets (MDH). Kansas State University’s radon program notes that homes with sumps or French drains can often be mitigated using the sump to collect radon (sosradon.org). EPA’s standards also require any sump that would let soil gas in, or let house air be pulled into a sub-slab system, to be covered and sealed (EPA, Radon Mitigation Standards).
On its own. A sealed cover is a form of sealing, and EPA does not recommend sealing alone to fix radon because it hasn’t been shown to lower levels significantly or consistently (EPA, Consumer’s Guide). Covering an open sump is still a sensible step. Test before and after, and if your level is still 4 pCi/L or more, you need a mitigation system. See also sealing cracks for radon.
What a radon sump cover must do
EPA’s Radon Mitigation Standards set out the requirements (EPA standards):
- Rigid and airtight. Made of durable plastic or another rigid material, and designed to seal airtight.
- Removable for pump service. Sealed with silicone or another non-permanent caulk, or with an airtight gasket, so it can come off when the pump needs work. If a radon pipe runs into the sump, it must have removable or flexible couplings for the same reason.
- Sealed penetrations. Holes for the pump’s discharge pipe, the electrical cord and any radon pipe are sealed with caulk or grommets.
- A window is a plus. Covers that let you see into the pit are recommended.
- Drainage kept. If the sump also collects water from the basement floor, the cover must be recessed and fitted with a trapped drain, so floor water still reaches the pit while air can’t pass through. Water traps should have an automatic supply of priming water so they don’t dry out.
- Submersible pumps recommended. Where a sump is used as a suction point, EPA’s standards recommend a submersible pump.
Buying one
Radon sump covers are sold by radon supply companies, home improvement stores and online. Before you buy, check:
- that it fits your pit’s diameter and shape;
- that it has a gasket or can be sealed with removable caulk;
- that it has sealed openings, or grommets, for your discharge pipe, cord and any radon pipe;
- whether your floor drains into the sump. If so, you need a cover with a trapped floor drain;
- whether it has a clear lid or viewing port.
If you have a radon mitigation contractor, ask them to supply and fit the cover as part of the system, and test afterward. To see how common high radon is in your area, look up your county below.