Thanks Chrystine. After visiting our local facility I've reached out to see if there are any bright ideas out there.

Good to hear the rationale for the schedule 40. I've only been using it indoors, with a schedule 40 muffler at the exhaust point. Thank you for the feedback as I search out a supplier...

I've sometimes fastened a cover with removable concrete anchors and used soft rubber tubing as a gasket between the cover and the concrete, run around the perimeter of the hole.

I have used Tyvek bags from my E-Perm dealer. They are cheap and come in a couple different sizes. They can be glued/taped shut and hung or tacked up as in the picture. I'm told they are "invisible" to radon and my own little test seemed to agree with that. Check with your alpha-track supplier if they are ok with that. Sorry, not a great photo.

I have had similar problems with Safety Sirens seeming to read high compared to my crm, or having a large spread in readings between units. In one instance, post mitigation, and with crm readings around 20, I eventually had three Safety Sirens (mounted on a wall) 8" apart with readings ranging from 40's to close to 200. Maybe radon is that finicky sometimes, and maybe mounting them on a wall isn't the best, but they've caused me some grief, especially in having to deal with remote locations where trouble-shooting is a little more difficult. I've also had problems, where the electrical power is perhaps dodgy, with monitors giving super-high readings, showing errors, or showing displays that aren't in the manual. I replaced with the battery powered option in those cases as well.

It looks like Yukon, Canada will be requiring daycares to test for radon as part of their licensing. This is a new thing here.

Thanks Robert and Karen. I was able to get some information from Radonaway. Yes, this is for troubleshooting mitigation difficulties and finding sources of radon, as opposed to monitoring for levels. Thank you for your feedback!