sub-slab depressurization system 2

https://wiki-canyon.win/index.php/How_a_Sump_Pit_Radon_Seal_Protects_Your_Home_from_Invisible_Threats

A sub-slab depressurization system pulls soil gases from beneath a concrete floor, using a fan to create negative pressure and venting them outside. It's a practical fix for radon or vapor intrusion, often involving a perforated pipe grid laid in gravel before the slab is poured.