46erjoe wrote:
The installers sealed the sump pump well with urethane foam.

What I hear you folks saying is that yes, radon can pass through walls
and floors

If the radon level was "just barely" over limit with large cracks in
the floor, then yes, sealing the large cracks thoroughly will very
likely reduce the radon level below the EPA recommended remediation
level.

Are you a non-smoker? Do you spend only occasional time in the
basement? You could just turn the fan off and stop worrying about it.
Impartial researchers and medical people with no monetary incentive to
fuel the scare campaign are skeptical of the radon hysteria.