"The right aquifer can vary wildly depending on the well level too. If the well is more full and that happens to be where the source of radon is, then you'll see a much higher reading."

I was wondering about that as a possibility too. If the water level inside the well was quite different between the two sampling periods, maybe the water level was below the source for the lower radon reading.

Then again, how deep into a well is a tester really able to go? I don't know anything about wellhead sampling, I'm guessing they don't go down very far.

Was it the same tester both times at the wellhead? Was the same methodology used both times? Is it possible the method the first time was performed poorly?

Thanks for the responses so far.

At this moment in time, I'm not familiar with any mitigators in PA that do anything like a heat tape or heat cable for any of their systems. Not sure that the regs would even allow for a heat cable to be installed on the inside of pipe.

I hadn't considered the possibility of large chunks of ice falling into the fan housing and clogging up the fan. Wouldn't that break fan blades? Also, in the event a large object was blocking the fan from spinning, would you expect there to be an unusual sound that would tell you something is blocking the fan?

I also didn't think about how systems moving more air are less likely to freeze compared to a system that relies on a low flow/high suction fan. So thanks for pointing that out.

Huh. I didn't realize it was Appendix AF now. For six years I've referred to it as Appendix F. I guess this is new with the 2021 version of the IRC?

As to the original question, there are a handful of municipalities in PA that adopted Appendix F. Maybe around 15 in the whole state. And they adopted it years ago. That's about it as far as I know.

I don't know if any of them updated to Appendix AF.

edit: I guess there were 18 municipalities that adopted Appendix F, last I checked one of them was working to remove that ordinance. Some of those municipalities hadn't seen any new homes built the year that I asked. One of them claimed they're pretty much "built out" already, I guess that means not much room left to build anywhere.

Delete this post please, repeat of above

Delete this post please, repeat of above

@Michelle: The main takeaway from the PA re-entrainment study is that we didn't find any real difference between ground level and roofline discharge.

There are a few things to consider. "Ground level" in this study was more like three to four feet above ground based on the system design. Still comfortably below roofline, but not actually right at ground level. The pre-mitigation levels weren't all that high (for Pennsylvania basements anyway), half had initial concentration levels at 10.0 pCi/L or below. The others were above 10.0 pCi/L. The exhaust gas concentrations, collected using Lucas cells and air pump with tubing going down the "throat" of the ground level discharge, were surprisingly low.

So does that mean you would expect re-entrainment with higher pre-mitigation levels/higher exhaust concentrations? Maybe. But maybe not. What if you have pre-mitigation levels above 100.0? Above 1000.0? Maybe ground level doesn't make sense in the latter case, but that would be a pretty rare situation. It wouldn't hurt to have more research.

Here are some of my personal opinions/thoughts after reading through this thread. I don't think there's going to be an end all be all study that answers our radon re-entrainment questions from now unto eternity. I also don't think the scientific method cares one whit about "consensus." What is a consensus today could change tomorrow. What won't change is the underlying reality, though our understanding (or lack thereof) is going to change over time unless we remain dogmatic.

So I wonder, is there enough data and compelling research to challenge the conventional wisdom of above-roof discharge and above-roof discharge only? Seems like things are pointing in that direction. I'm not claiming to know the answer, but I'd be happy to see more discussion/debate/questioning around the issue.

On behalf of Bob Lewis, manager of state radon program in Pennsylvania, I am posting a link to the final report of our re-entrainment study.

Radon Re-entrainment Study – An Initial Investigation

Thank you. If anyone has any other illuminating information, please do share.

Not having read the articles Kevin posted, I'll assume for the moment the hypothesis that air filtration may actually *increase* the risk that indoor radon poses is true.

Is it still fair to say that increasing air movement within a space is likely to lower the working level in said space? I've been operating under the assumption that something as simple as ceiling fans or box fans would cause RDP to attach to particles in the air, and thus lower the working level. Would love to hear some feedback on this thought.

Ignoring the part about radon, but I assumed an air purifier would filter out decay products from the air. So you're saying instead it will detach decay products or prevent them from being attached? Seems totally counterintuitive to me but if you or anyone else could point me to that research I'd be interested to see it.

Interesting question. I'll take a stab, if anyone finds something wrong, feel free to correct me.

Radon, though radioactive, is a noble gas. Which means it's chemically inert. It doesn't really interact with anything, although it sticks to charcoal for some reason because apparently everything sticks to charcoal (I'd love for someone to explain that bit to me). The only real leakage you would be concerned with is not having an airtight system where air, including radon, would get pushed/pulled into the house. I assume PVC is non-porous so that you won't have any emanation through the piping material, so as far as I know, so long as you have an airtight system, nothing is going to "leak" into the house.

But since you got me thinking about it, I wonder how much of the radioactive decay products, which are "sticky," end up sticking to the inside of the PVC pipe. I wonder, if you've had a system that's been active for a number of years, or if you have active systems that are mitigating houses with extraordinary radon sources, how much of the decay products are deposited throughout the system. Maybe you would be able to detect gamma coming through the system piping/fan housing? Hmm. Just thinking out loud here.

Bill "Brilliant but Brutal" Brodhead.

Can't say I'm a fan of such a morbid massacre, yet at the same time, I can't really cast judgment. Those things are nasty.

Just try not to step on that pile of stingers. Ouch.