Any buyer with less than **** for brains is going to insist that this
be corrected properly, by a professional company, not the homeowner and
that a further test shows that the radon is now at an acceptable limit.



yeah as a relatred issue I want to install a interior french drain, the
home is above the grade of the street. I have wondered if draining the
french drain by gravity to the street and adding a couple fresh air
vents would allow the radon to leave naturally?

the reason the OP vent didnt work is that radon is heavier than air, so
it comes out in the home rater than on top of the house. roof vent too
high

in any case he will have to use a certified radon company at a cost of
about 2 to 3 grand depending on how many vents are needed

also minimizing vacuumn in the house like hot water tanks and furnaces
using indoor air, that tends to suck more radon in.

using outdoor air for combustion is much better