radonmonitorguy

Not OP but I can help you out. Radon is a byproduct from the breakdown of natural radioactive material in the earths soil. It's literally everywhere. There's really no "radon-heavy" areas. Your house could test at a 10.5 pCi/l which is above the EPA recommended action level at 4.0 pCi/l and your neighbor could test at a 2.0 pCi/l, there is really no way to know what your house will measure at until you get it tested.

I actually work for a company that manufactures radon monitors, What type of devices are you using to detect the radon?

I'm not OP but I may be able to help you out on the test results part of it, the way radon works is very unpredictable, so with your house testing at a 3.1 then a 2.1 is a very common occurrence. Radon has a pattern where it is higher at one point of the day and lower at the other point, especially if you don't have a mitigation system. Weather is a big factor of it as well. Radon cant move through water so if it was raining or had rained at some point before the test was conducted, may have caused a false high reading in the first test. Also depending on what they used to test your house, say if it was a charcoal canister, something could have happened on transit to the lab, such as accidentally being exposed to outside air, giving a biased reading.

As OP says every home is at risk. Usually radon will half in concentration per floor so someones basement can test at a 5.0 pCi/L and the floor above that will be at a concentration of 2.5 pCi/L a lot of the times. If you don't have a basement then you are getting the full amount of radon that is finding its way into your house.