ELEVATED RADIOACTIVITY IN GROUNDWATER IN SOUTHWESTERN VERMONT

The Clarendon Springs Formation is an Upper Cambrian dolostone that is found in a narrow north-south belt in western Vermont. Elevated levels of radioactivity in groundwater have been associated with the Clarendon Springs Formation in northwestern and west-central Vermont. It is the aim of this study to see if such a correlation exists in the region of the type locality of the Clarendon Springs Formation in southwestern Vermont.

Preliminary results (gross alpha analysis for 18 groundwater samples; 17 from private wells and one from a public water supply) indicate that there is some elevated radioactivity in groundwater in areas that have been mapped as Clarendon Springs Formation. Six samples have gross alpha results above the Vermont drinking water standard of 5 pCi/L. One of these wells has been sampled for analysis of radium 226 and radium 228. The combined Ra-226 and Ra-228 is slightly below Vermont’s drinking water standard of 5 pCi/L. Another home with a gross alpha result above 5 pCi/L has identified elevated radon levels. Two of the eighteen wells produce from overburden (gravel); these have very low levels of radioactivity.

Determining the correlation between elevated radioactivity in groundwater and the Clarendon Springs Formation is hampered by a lack of outcrop, as well as by the variable nature of the Clarendon Springs Formation. However, one outcrop that was positively identified as Clarendon Springs Formation was sampled for bulk rock analysis. A flaky “gouge”-like material filling a fracture contains 34.7 ppm Pb. Another outcrop sampled for bulk rock analysis from the region of groundwater sampling contains 24.8 ppm Pb.

Determining the degree and extent of radioactivity in groundwater is valuable as a public health service. The results of this study are shared with homeowners as well as becoming part of the larger study of the Clarendon Springs Formation in western Vermont.