Sorry to hear about your radon scare, I went through this myself a few years ago after we bought a house with a basement. I bought a radon detector and was finding a long term avg of about 8 pCi/L. EPA says take action at 4 pCi/L. Rest of the house was fine, didn't address it immediately as we didn't go down there much. When we decided to finish the main basement area and turn it into a big play room for the kids, radon was back on my mind.
Attempt #1
I figured most of the radon was probably coming up from the open sump pit. So I sealed the pit airtight and ran a 2" vent line outside. No fan. This dropped the long term down to right at 4 pCi/L. This was nice improvement, but with the kids being down there a lot now, and playing on the floor, often laying on their bellies I was still concerned.
Attempt #2
There was a 3" PVC pipe coming out of the basement floor and venting out to the roof, so some type of foundation vent. Maybe even a passive radon vent. So I put a radon fan on it, no change, not even a little.
Attempt #3
I put a radon fan on the 2" vent line installed in Attempt #1. Long term radon levels dropped to around 0.6 pCi/L). My biggest concern is if the fan sucked out the water from the floor drain, or if the floor drain dried out, the fan could suck air from within the house. Putting the house in a negative pressure. Since I have a gas furnace this could potentially suck flue gasses back down. I previously installed a fresh air intake on my furnace return air, so my house runs at a slight positive pressure and has a small percentage of fresh air coming in anytime the HVAC runs. Also, my french drains daylight to the basement window wells, so pretty steady source of inflow air for the fan. I used the smallest readily available fan I could find and have CO detectors on all levels of the house linked to my phone. I also have a dehumidifier dumping into floor drain. It moves less air than our dryer, so probably me over thinking, but that's what I do. Spent less than $200 on everything. No problems for several years now.
Any advice about visiting the Atlanta Zoo?