After 48 hours, it turned on, beeped and displayed.. 4 pCi/L ! Just one over the limit.
So, I lowered the detector back down near where it was before. About 2" off the floor. (see right frame).
It displays "--" for 48 hours after a reset.
That 39 pCi/L reading was obtained with the detector tied to the PVC pipe
right above the hole. (Which isn't a good method, per the manual).
But, I had measured the another one of the new sump holes same way and never got above 3 pCi/L..
And, a third sump hole with the detector a little higher. 16" & it was also 3 pCi/L