Geochemical Analysis and Origin of Uranium in Groundwater Wells in the Clarendon Springs, Skeels Corner, and Danby Formations, Colchester/Milton, VT, Poster 54

The main goals of this study are to: geochemically analyze groundwater from bedrock wells in a carbonate-dominated aquifer with elevated radionuclides (uranium and alpha radiation); determine mineralogical and chemical... [ view full abstract ]

The main goals of this study are to: geochemically analyze groundwater from bedrock wells in a carbonate-dominated aquifer with elevated radionuclides (uranium and alpha radiation); determine mineralogical and chemical signatures of the main bedrock units; and assess implications for local groundwater flow and potential migration of radionuclides. Prior research by the VDH and VGS showed that 23 % (30/131) of wells in the Cambrian Clarendon Springs Formation (Ccs) contained gross alpha radiation above the EPA MCL of 15 pCi/L, with many wells > 100 pCi/L. Uranium is similarly elevated. The two adjacent formations, slates of the Skeels Corner (OCsk) and carbonates of the Danby (Cda), have not been studied in depth, but may be sources of radionuclides, or contain radionuclides carried by groundwater flow from the Ccs.

In Ccs groundwater, alpha radiation exceeds 15 pCi/L in 8 of 14 wells (mean = 54 pCi/L), and 6 of the 14 wells exceed 20 ppb U (mean U = 43 ppb). Wells upgradient in OCsk slates yielded very low U and alpha, but did yield elevated strontium levels (three times the Ccs average) that makes Sr a good tracer for OCsk groundwater – this tracer reveals groundwater flow from OCsk to Ccs that appears to dilute the U and alpha radiation in Ccs wells adjacent to the OCsk. Wells in the Cda downgradient of the Ccs yielded elevated uranium (4-23 ppb) and alpha radiation (4-13 pCi/L), indicating that on scale of up to 5 km, radionuclides may be transported to adjacent units.