RADON POTENTIAL OF THE UTICA AND MARCELLUS BLACK SHALES OF EASTERN NEW YORK

Radon is a naturally occurring radioactive noble gas that is the second leading cause of lung cancer in the United States. Radon, a decay product of uranium, is emanated from uranium-bearing rocks, including marine black shales, and transported through pore space into homes. Marine black shales are rich in hydrocarbons and thus are a major economic target for their oil and gas, but are also pose a health hazard due to the emanation of radon. Radon is not combustible or soluble, and can enter homes when natural shale gas is burned in a stove, or when radon-bearing groundwater is released through a faucet. The Ordovician Utica Shale, has an areal extent of ~440k km² in the eastern United States, and the Devonian Marcellus Shale, ~264k km² in extent: both targets for hydrocarbons. Although different ages, both units were deposited in anoxic marine basins and thus are rich in total organic carbon and uranium. The Utica Shale and interbedded bentonites has reported values of ~8-20 ppm U and and 14-63 ppm Th (Delano et al., 1990), and the Marcellus Shale has reported values of ~6-85 ppm U to 6-17 ppm Th (Leventhal et al., 1981). In many instances, there may not be a straightforward relationship between uranium concentration in rock and radon emanation rates due to mobility and redistribution of uranium. There is abundant evidence that in black shales, uranium has been liberated in the rock, mobilized by fluids, and reprecipitated along fractures. We are not aware of any measurements (U, Th, or radioactivity) on the surfaces of cracks and fracture planes Thus an important question concerns deposition of either uranium (or radium) along cracks and fractures that are then in intimate contact with groundwater or other fluids. A hypothesis that is being tested in this ongoing study is whether there are differences in radon potential in fractured bedrock, or along cracks and fissures. This study is focused on measuring relative radon emanation rates and in situ radioactivity from black shale in four sections of eastern New York (Chuctanunda, Canajoharie, Cherry Valley, and Cobleskill). Radon is measured from crushed samples using CR-39 and LR-115 alpha track detectors and gamma ray spectrometry (using portable Gamma Spectrometer) is being used to evaluate total radioactivity of U, Th, and K (in µR/hr).