[Dragonfly DIY] Radon remediation system

I recently re-discovered a radon test I'd done a few years back. The results were 8.8, and the EPA action level is 4, I don't know why I didn't do anything at the time, probably it just slipped my mind, but I decided to do something about it now.

A bit of research showed that for relatively new houses like mine (20 years old) where the basement slab is on top of gravel, the proper remediation is to install a fan system that applies a vacuum to the gravel layer under the slab. This has the effect of removing the high concentration of radon before it can seep into the basement and the house and exhausting it into the outside.

The house has a sump well, which drains perforated tile ("weep tiles") around the perimeter of the house from the gravel. Venting this is an ideal solution. In houses without this, the solution involved coring a large hole into the concrete to get access to the gravel layer underneath, then sealing a pipe into that. Owners of even older houses may face more difficulties in coming up with a working system.

The sump well is sealed with a big molded plastic cap, through which are holes to allow the sump pump and wires to go through, and in my case also the drain for the water softener. The 3 inch PVC pipe for the radon vacuum system goes into a screw fitting on the cap.

I had to do a little fiddling with the sump pump piping, it was too low to the ground to allow the cap to fit under.
I cleaned the concrete with a wire brush to get good adhesion and laid down most of a tube of PL300 adhesive. That's intended for foamboard but rated to stick to concrete and I figured it'd be good to stick down plastic. Seems to be working.
Note that there's a rubber joiner on the big pipe there, the check valve on the little pipe unscrews and there's a rubber join on the little pipe inside before it gets to the pump. This will allow for removal of the cap to service the sump pump.
I also tapped power from the outlet that the sump pump was plugged into, that's the conduit you see going along the wall there. It goes up to a switch on the wall, then to a box which goes to the waterproof whip that goes outside to the fan:

The big vent pipe goes up and over to the point where it exits at the sill plate. The manometer is up there too - it's the blue U shaped thing. This is tapped into the tube and gives you an indication of how well the vacuum system is operating.

Outside the house is the fan itself. It is designed to allow rainwater to pass through without bothering the motor. The blower itself is a radial blower arrangement underneath a cap so the water just goes around the whole motor/blower assembly. Also note that the pipe and power whip are both caulked (inside and out) and that the power whip dips below horizontal before entering the house - this allows rainwater to drip off the bottom rather than trying to run into the house.

Finally the pipe exits above roof level.

And finally, I have a floor drain that is at the end of a 4" piece of corrugated pipe that is used to catch condensation from the 90+ furnace and the A/C, and also overflow drip from the humidifier on the furnace. Obviously a 4" gaping hole in the system would defeat the purpose. My solution for this, since this drain only needs to accommodate small slow drips, was to 3D print a sort of inverted top hat with a funnel at the bottom, ending in a 4mm hole, which is plenty to allow drainage but shouldn't be big enough to really affect the suction of the radon system. I need to do a little fiddling on the pipes going into here, it's kind of a big mess caused by the installers of the various systems and it needs cleaning up. But it seems like it's doing the job.

So, does it work? Seems to be. I bought a digital monitor, which I installed a couple days before I finished installation. The monitor takes 48 hours to fully adjust. Just before I flipped the system on, it was reading 20, which is 5x the "take action" point.

The reading goes up when it rains - I assume the rain is either liberating gas to infiltrate, or drives it in to the building. But anyway, when it was dry, the meter read 0.02 - down 1000x from the regular reading. When it's raining, it goes up to 0.32 but that's still within very safe range.

With the reading this low, I may play around with installing a timer and running the fan at a lower duty cycle, as I have seen others doing online. The meter should allow me to judge whether it's safe to do so. I will probably start with something like 2 hours on, 2 off. It'd be really fun to work it into some automation that would run constantly when it was raining, then back off when it was dry. I'd really like to tie it in to the radon monitor, but I couldn't find any that had any connectivity.

Project costs:
Radon kit - with fan and manometer at home improvement store, $127
Radon sump dome - $90
PVC, conduit, wire, switches, cable whip, etc: guessing about $75
Digital radon monitor - $200

The radon monitor is perhaps something that can be skipped, but I decided that if I am going to do this, I want to know if it's working.