This is a graph of radiation levels on Warren St in North Adams. Natural levels in Massachusetts are around .01 mrem/hr. If there's a spike at the beginning ofthe graph, ignore it - that's an artefact of the geiger counter powering on.
There are three kinds of radiation - alpha, beta, and gamma, each with different risks. My counter counts all three but doesn't discriminate, so I convert counts-per-minute to rem as if the radiation were from Cobalt-60. As a result, these numbers are approximate.