My Radon is:
4.0 for the 48 hours.
3.2 for the week.
2.6 for the month (and year).
Over a week ago, we got some snow, twice. Since last Friday, we've had melting of snow during the sunny days. So, the Radon has been up and down, averaging around 4.0 with the chart showing more red peaks than yellow dips.
It seems like any water going into the ground causes a Radon peak. Even small amounts. If the ground is already pretty saturated with water, it doesn't seem to take much water going down to send up a bunch of Radon.
The water table here is very close to my basement floor. I have a large pond nearby. So, when it rains, we sometimes get radon quickly.
However when the water table is lower, it can rain like crazy and we get nothing. But
occasionally 24 to 48 hours later, the Stump Pumps start running! When it's sunny outside!
Regarding the air pressure. My house has an exhaust fan in the kitchen, a oil burner and a clothes dryer in the basement. Any of them can lower the pressure inside the house, causing radon to flow into the basement.
Radon is heavy, so it will pool on the floor like leaked Propane.
That's when I turn on the Radon pump in the basement.
If you have a radon pump or other blower etc to move a good volume of basement air outside, your average should be okay.
At the kid's house, I have their radon pump on a timer, so it's not running full time. I leave it off late at night. It runs during daytime, when people are using the basement. The Radon (was 27) stays between 3.0 & 4.0 almost all the time. If it starts going over 4.2, we run the pump for longer hours for a few days. (Their detector beeps at 4.2). Rain causes peaks there too.
I'm not sure if the New Geothermal GSHP well (or wells) 30 feet away from their house does anything to their radon levels. It's really just lowering the temperature of the groundwater.
If it's a closed loop system. WHo knows?
It's just across the narrow street in front of the house.
Cheers,
Rich