URANIUM AND 222RADON IN GROUND WATER FROM SELECTED GLACIAL AND BEDROCK AQUIFERS IN THE NORTHERN UNITED STATES

Regional occurrence and distribution patterns of uranium and ²²²radon were analyzed using data from 1,200 monitoring, public, and domestic drinking-water wells in glacial, Cambrian-Ordovician, and fractured crystalline-bedrock aquifers throughout the northern United States. These data, collected as part of the U.S. Geological Survey's National Water Quality Assessment (NAWQA) Program, show that at a large regional scale, uranium and ²²²radon concentrations vary with the geologic source of the rocks comprising the bedrock aquifers. For the glacial aquifer system, these concentrations vary with the geologic source and origin of the unconsolidated deposits that form the aquifers.

Uranium concentrations greater than 1 microgram per liter (µg/L) were measured in 36% of 1,200 ground-water samples. Twenty-eight samples exceeded the U.S. Environmental Protection Agency's (USEPA) Maximum Contaminant Level of 30 µg/L. Nineteen of the 28 samples were collected from wells in glacial aquifers derived from predominantly Cretaceous sediments in the north-central United States; 4 samples were collected from wells in glacial aquifers, which were derived in part from basaltic lava flows, felsic igneous rocks, and paleo-lakebed materials in the Columbia Lava Plateau in Washington State; and 5 samples were collected from wells in bedrock aquifers derived from felsic igneous and metamorphic rocks in the New England crystalline-bedrock aquifer. The highest uranium concentration (429 ug/L) was in a sample collected from a domestic bedrock well in New Jersey.

²²²Radon concentrations exceeded the proposed USEPA drinking-water standard of 300 picocuries per liter (pCi/L) in 60% of the 1,200 ground-water samples. Thirty-four samples exceeded the USEPA alternative drinking-water standard of 4,000 pCi/L mandated for community-supply systems. Thirty-three of these samples were collected in domestic wells from the New England crystalline-bedrock aquifer and one sample was collected from a domestic well in a northeastern glacial aquifer. The highest concentration of ²²²radon (215,000 pCi/L) was from a domestic bedrock well in New Hampshire. In this regional study, the geologic composition of the aquifers was a more important factor affecting uranium and ²²²radon occurrence in ground water than local geochemical conditions.