good job on the VB installation
there is a spec on the DOE website for a PVC vent pipe to take the radon gas out of the crawlspace-the pipe vents off the gas to above the roofline to keep everyone healthy.
were you wearing masks during the install?
Yes, mitigation unit has a fan. It depressurizes at 1.5 to 2.0 in-H2O. It blows out.Does the mitigation unit have a fan? Maybe it is blowing the wrong direction.
are you saying you HAVE this in place (VB instead of concrete) and still getting the air pocket? might have to put pea gravel ontop of the plastic to keep it down. What if had put down gravel first, then the plastic, which might allow the gas to find its way to the piping out of the space. note: not sure if it would work
My guess is that you did such a great job sealing the vapor barrier, the heat from the ground is trying to balance the temperature of the crawl space and can't escape. If the ground is emitting 50deg and outside temp it 30deg. warmer air is going to rise and get trapped.
The only solution I see is as described previously-add pea gravel over the entire area to hold the barrier down. Surface area to surface area, your perf. pipe is not going to be able to exhaust the volume of air fast enough to hold it down.
One way to test my theory is to get a job heater or two and warm up the crawl space. If the barrier goes down, you know your answer. If it stays up, then pipe out whatever is under there and see if it burns-you may be sitting on a natural gas well!!!!:laughing:
Kicker is even with the crawl well sealed AND a mitigation unit installed, radon levels are still at 15pCi/L.:blink:
are you saying that the crawlspace does have a pipe heading outside? seems I understand it's not, in which case the built up radon has to go somewhere-it's only going to push the VB bubble so far before it finds a path of least resistance-through the soil, pours in the block wall or somewhere else. doesn't seem moisture is the issue, in which case the space needs a pipe heading above the roofline to get the radon out.
let us know what it takes to finally get the level down.
Extending the mitigation existing mitigation system to the pipe that was placed under the plastic in the crawl space will pull the air out from under the plastic and the plastic should be pulled down tight...
Is the water level in the sump pit above the sump pit drain tile? According to your drawing, the water level is below the drain tile. If the water level is consistantly above the drain tile, the mitigator is correct. Can the sump switch be adjusted to lower the water level? Has the mitigator conducted what we call pressure field extension or comminication tests to see if there is suction beneath the slab? This is accompolished by drilling a .5 inch hole through the slab a distance away from the suction point - sump pit- and using either smoke or a micromanometer to measure the pressure differential above and below the slab. If the smoke goes down the hole or the micromanometer shows negative presssure, you have suction under the slab and the radon is coming into the house from another entry point.
If the water level is even with the bottom of the drain tile, you should have suction under the slab. I would check pressure field extension to be sure and get the system extended over to the crawl. If these actions don't solve the radon issue, there are other things that can be checked.