Are these changes needed?
My two cents on ground level discharge.
I did not work on any of the first PA houses, but there were some pretty funky internal walls that were entry points in those houses. I was involved in all of the next set of houses in Clinton NJ. Those houses were in a neighborhood where houses were in multiple 100's. All homes were built by same builder on a few floor plans so information from one house was then used on the others and there were public meetings so homeowners could use the research houses to mitigate there own. We were in the basement of one of these houses where the mitigation was not getting the radon levels down below 4. There was a concern that there was re-entrainment with discharge behind the shrubs outside the house. Someone put dryer vent on the exhaust to run it past the shrubs and away from the house and we watched the radon level drop on the CRM.
Bruce Henschel did an amazing job developing the encyclopedic Mitigation Manuals, but models are only as good as the data input into them and need to be used with caution. For almost 20 years the VI folks did not look at pressure driven flow into the buildings even though the radon folks knew it existed. Their models did not show it and as late as 5 years ago the standard radiation models used on contaminated sites still did not include it - only included diffusion through the slab.
I saw re-entrainment from a high level house with shrubbery around it - it is clearly possible. Will it happen in a house below 10 - maybe not that we can measure, but what radon level is safe for ? Is it a function of the inside radon level or the soil gas number?
If there is a lot of sealing that results in only slightly elevated radon levels in the home, will we have any idea if the soil gas levels are very high. As with much of radon - it all depends.
It seems to be an area where significant research could lead to an answer, which might be one thing for radon, where we have good options for real-time monitors and a different answers for VI where we don't. And as discussed above, that may only apply to single family homes with larger lots and not urban/suburban areas where homes are closer.