Yup, based on an old thread here I bought an Airthings monitor and kept tabs on things. The 365 day average was about 220/bq m3 for the longest time which was borderline. Then 2 years ago after a new HE furnace things went to about 270. Levels are seasonal, and in hot weather things would peak at 365 which finally convinced me to do mitigation work.
Based on recommendations here I had Radon West do the work, even if it meant waiting. These guys really sweat the details in a very methodical approach. They did a stellar job - doing what Silver described, but also sealing up other massive openings in the slab. It was a surprise to learn about big holes in the slab below the furnace, the basement P-trap, and other places. Because of these variances in construction - it's not a guarantee that every house on the block has or doesn't have an issue even if you do.
Levels are about 25 right now post mitigation. You're also given an official 3rd party lab test kit after the mitigation so you can demonstrate to any future buyer the problem is solved.
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