Sump Pumps & Radon Mitigation: The Unsealed Pit Problem
You hire a contractor to install a radon system. The first thing they do? They walk straight past the foundation walls and stare at your basement sump pump pit. Why? Because an open sump pit is the fast lane for soil gas.
The Sump Pit is a Direct Highway into the Soil
Most basements are constructed with a concrete slab resting over a bed of crushed gravel and dirt. To manage groundwater, contractors dig a deep hole (the sump pit) directly into that dirt, installing a pump to push water out.
If the homeowner leaves the pit open or covers it with a cheap, unsealed plastic lid, thousands of cubic feet of soil gas—including toxic radon—free-flows directly into the basement air.
Why You Cannot Install a Radon System Without Sealing It
A standard Active Sub-Slab Depressurization (ASD) system works by drilling a 4-inch hole in the concrete, dropping a PVC pipe in, and using a roof-level fan to aggressively suck the radon out of the gravel bed underneath your floor.
But vacuum physics dictate that suction follows the path of least resistance. Provide an open sump pit nearby, and the radon fan will simply suck the conditioned air from your basement, down the pit, under the concrete, and out the exhaust pipe. You will lose hundreds of dollars in heating and cooling energy, and you will not depressurize the soil gas. You must seal the pit to "close the loop" of the vacuum under the house.
The Solution: Air-Tight Sump Domes
- Bolted Lids: Mitigators replace cheap corrugated plastic covers with heavy-duty polycarbonate domes, bolted directly to the concrete surrounding the pit.
- Silicone Seals: The perimeter of the dome is sealed with 100% silicone or polyurethane caulk.
- Rubber Grommets: The water discharge pipe and electrical cords passing through the lid are sealed using thick rubber grommets.
- Bonus: Using the Pit for Suction. Sometimes, the mitigator will run the 4-inch radon PVC pipe directly into the sealed sump cover itself, using the massive pit as an incredible suction point for the whole house!
How Much Does Sump Pump Sealing Cost?
If done simultaneously with a radon mitigation system installation, sealing a standard sump pit typically adds $150 to $250 to the total invoice. This covers the cost of the heavy-duty clear dome cover, grommets, caulk, and a half hour of labor.
Does your basement layout include a sump pump?
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