FYI, an interesting new web page is at URL http://www.normis.com/nindex.htm
The TENORM Page, by Phil Egidi (firstname.lastname@example.org)
NORM stands for "Naturally Occurring Radioactive Material" and
TENORM stands for Technologically-Enhanced Naturally Occurring Radioactive Material."
Dose rates rise gradually as soil dries out. Water shields the radiation coming from the NORM in the ground, and dilutes the concentrations of NORM in the soil. After rainfall, the background values drop.
Rainfall scours radon and its progeny from the atmosphere, causing radiation levels to rise at ground level. Some larger storms may double the gamma exposure rate for a short period of time.
The shielding effect of snow is substantial (Fig. 4.). Shielding is dependent on the water equivalent of the snow because a heavy wet snow is more effective at shielding than a dry snow.
Month-to-month variations in background are due mostly to changes in soil moisture content and snow cover. Winter months trend to lower radiation levels because of higher soil moisture and summer months trend toward higher levels because of lower soil moisture. Seasonal effects actually average out over the course of a year
Cosmic ray variations tend to be small and result from changes in barometric pressure. With a high pressure system, there is a larger mass of air to provide a shielding effect, as compared to a low pressure system, which has less air mass and less shielding.
Seasonal changes also occur in the deposition of cosmogenic radionuclides on the ground. Deposition is greater during the spring months when air in the stratosphere mixes with air in the troposphere, where it gets washed out by precipitation.
A review comment from RADSAFE:
"...an extensive site (50-70 pages), fully footnoted and
referenced with lots of links to other NORM sites."