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Radon Potential Map Explanation

     Area radon potentials are from a computerized spatial analysis of bedrock geology, surficial materials, and
surface radioactivity mapping, with indoor air and bedrock well water data. The radon data includes 4721
homes and 958 bedrock wells tested for radon statewide between the years 1985 - 1995. The testing was
conducted by the CT Department of Environmental Protection, CT Department of Public Health, U.S. Geological
Survey, University of Connecticut and the Stamford Department of Health.

     Radon measurements have been correlated with geological and geophysical factors enabling the mapping
potential. Digital resource maps were scored separately for radon potential, and compared to indoor air
analyses to determined the usefulness of each resource map for the prediction of radon. The radon potential
map is a summation of radon scores developed from these earlier analyses.

     Surface radioactivity measurements provide summary information for total gamma emissions from all areas of
the state. There is a direct correlation between surface radioactivity and average indoor radon. Area with
the highest surface radioactivity correlate with areas of highest average indoor radon and are therefore
scored with the highest radon potential.

     Surfical materials units are used as a measure of surface permeability and potential radon transport to the
surface. As such, surficial material units are assigned radon scores according to their texture. Areas of
coarse-grained sediments are assigned higher radon source than areas of fine-grained sediments. Each
bedrock unit is assigned a radon score based on the average radon in well water of that unit, or by
reference to similar geologic units.

     The scoring strategies have been tested by comparing radon scores for each component resource map with
indoor air radon data. Each of these scoring strategies provide a positive correlation between average
indoor air and the assigned radon scores of individual mapping components. The areas of more permeable
sediments, higher bedrock well water radon, and higher surface radioactivity have higher average indoor
radon.

Scores for Component Resource Maps

Radon Potential Score	5	4	3	2	1
Surface Radiation (counts per second gamma)	> 900 cps	900-700 cps	700-500 cps	500-300 cps	<300 cps
Surficial Materials	----------	gravel & coarse sand	mixed sands	mixed fines	fines & clays
Bedrock Well Water	> 10,000 pCi/L	9,999-5,000 pCi/L	4,999-3000 pCi/L	2,999-300 pCi/L	<300 pCi/L

     The combined scores of component resource maps create a total radon potential score for each area of the
state. These scores range from totals of 4 to 13. Frequency analyses show a progressive increase in average
indoor radon with total radon potential score.

     The total scores are grouped into 4 categories by similar average indoor radon. These categories are shown
on the map as radon potential ratings. These radon potential ratings describe areas of statistically
different indoor radon levels.

     Sites of naturally occurring radioactive minerals referenced in the geologic literature are approximately
located on this map where possible. These sites include an assemblage of various minerals which may produce
locally high radon. These sites are included on the map for reference and are not part of the development
of the radon potential ratings.

These mineral locations may be useful tools in the development of regional and local level radon potential
evaluations.
 

Source: Connecticut Department of Public Health