Radon is present in the brine that is mixed with fracking fluids that return to the surface after injection at shale gas wells (
http://www.museumoftheearth.org/files/marcellus/Marcellus_issue4.pdf). This article refers to the Marcellus deposit in NY State as well as one in Texas, but there are many wells in the midwest that should be similar. According to this, higher radiation on a sensor lowered into the wells is used to detect the depth of the shale layers, because radioactive elements tend to concentrate in living organisms which are the original source of the oil/gas. Decay into soluble Radon puts it into the ground water at that layer, and mixing with the injected fluids can bring it up to the surface.
Has anyone brought a geiger counter to tailings ponds? Is it possible that the short-lived spikes we are seeing are due to drilling/fracking activity at upwind fields? Shale wells are at
http://shalebubble.org/dbd-map/.
_________________https://netc.com/chart/view.php?n=1%3A919A925A.5 Toronto, Ontario, Canada SBM-20 indoors