Is Sealing the Sump Enough?
In many circumstances, radon mitigation of a residential property has two main components: 1) sub-slab depressurization 2) the installation of a sealed cover on the groundwater sump.
We are often asked if installing the sealed sump cover will be enough to address the radon levels. In our experience, the vast majority of the time the answer is no. In circumstances where we have installed a sealed sump cover as a stand alone measure, and completed follow-up measurements, invariably the results indicate sub-slab depressurization is required.
This is not to say that the installation of a sealed sump cover won't improve radon levels. It can. But it is not likely to move the needle sufficiently.
If the sealed sump cover doesn't really help lower radon levels, why do it? A sealed sump cover is necessary where sub-slab depressurization will be employed. When we induce a negative pressure under the floor slab, basement air will be sucked into an open sump. This is not the air we want, we want air under the slab (soil gas). Sub-slab depressurization can still work with an unsealed sump, but it can greatly impact system efficiency and may lead to conditions that make it difficult for some combustion appliances to operate properly.