In homes with a basement or homes built on a slab, radon problems can often be mitigated with a modified sump pump system. In such a system, perforated pipes located beneath the slab drain excess groundwater into the sump pit. Radon is also collected from these pipes. A cover with an airtight seal is placed over the sump pit, and the radon collected is vented through a pipe and released into the outside air above the roof.
Removing radon with a sump pump is one of the more popular methods for radon reduction. This type of system can be retrofitted in homes where a french drain or drain tile system has already been installed to prevent groundwater seepage. It is important to note that sump pump systems that have not been retrofitted for radon removal can actually release more radon into the home through an uncovered or improperly covered sump pit.
The most important features of a system designed to remove radon with a sump pump are a submersible pump and a tightly-fitting cover. The sump pump cover should be made of a durable material, such as ABS plastic or acrylic glass. Ideally, the cover should be transparent or have a window through which the sump pit can be viewed. In case the pump ever needs to be replaced or repaired, it is a good idea to seal the cover with silicone caulk because it is easily removed.
A vertical pipe, usually made of schedule 20 PVC, is inserted into the cover to allow the radon to vent to the exterior of the home. Usually, the vent pipe releases the radon collected into the air above the roof. Just as the cover needs an airtight seal with the sump pit, the pipe should have an airtight seal with the cover. If a properly-fitting rubber gasket does not create an airtight seal between the vent pipe and the opening in the cover, more silicone caulk can be used to fill any gaps.
When removing radon with a sump pump system that has been retrofitted, another consideration is whether the existing system was designed to remove surface water. Some sources of surface water handled by a sump pit include flood water from heavy rain or waste water from a washing machine. The sealed cover placed on sump pits used to remove radon would normally prevent surface water drainage. To allow surface water to drain, a special drain pipe can be installed through the cover that allows water to pass through to the sump pit, but prevents radon from escaping through the drain pipe into the house.
Both passive and active designs are used for systems that remove radon with a sump pump. Active systems make use of a radon fan, located in the vent pipe, to encourage the radon to move up the pipe and out of the house. Passive systems do not have a fan, but depend instead on natural convective air flow that causes warm air to rise up and out. Depending on temperature conditions inside and outside the home, a passive system may be a more or less effective way to get rid of radon.
Although homeowners can design and install a system that will remove radon with a sump pump, having it professionally installed may provide better results. In the US, the Environmental Protection Agency recommends that homeowners contact their state radon office for advice on how to best mitigate their radon problems. This office can also provide references for qualified professionals experienced in removing radon.
To ensure effective operation, it is a good idea to test radon levels before and after installing any radon removal system. Radon levels are generally considered acceptable when they are below 4 picocuries per liter (pCi/L). Even homeowners with radon levels between 2 pCi/L and 4 pCi/L may feel more at ease with a radon mitigation system in place.