ABSTRACT
The Connecticut Geological Survey within the State Department of Environmental Protection (DEP) is working with the State Department of Health Services (DOHS) investigating the occurrence of radon in Connecticut. In 1985 and 1986, approximately 300 private and public water supply wells from 20 geological areas were tested for radon by the Toxic Hazards and Public Water Supply Sections of DOHS. Highest ground water radon was 130,240 pCi/l from the Nonewaug Granite, a two-mica granite (range 10,720-130,240 pCi/l). Elevated radon was found in wells within several granitic gneisses: the Glastonbury Gneiss (3070-80,900 pCi/l), the Canterbury Gneiss (10,010-64,510 pCi/l), and the Hope Valley Alaskite Gneiss (4060–59,180 pCi/l). These Paleozoic and PreCambrian age rocks underlie ∼5% of the State. Intermediate radon levels were found in water from PreCambrian and Paleozoic age stratified metamorphic rocks where radon levels> 10,000 pCi/l were widely scattered in these surveys. Relatively low ground water radon values were found in central Connecticut Mesozoic age sedimentary rock wells (390-8490 pCi/l) and in Paleozoic age carbonate rock wells (200-4130 pCi/l).
Preliminary results from the ground (carborne) gamma radiation survey generally show a positive correlation with radon water analyses, enabling characterization of geological areas in Connecticut as radiation sources. DOHS is currently conducting 2,200 air tests in homes located in geologic areas selected from water analyses and the ground survey. All data is compiled on 1:24,000 maps to be included in multiple natural resource spatial analyses using an automated Geographic Information System. The analyses will explore relations between the distribution of radon levels and earth materials to better define the geologic areas and possible origins of radon in ground water and in indoor air.
