HIGH LOCALIZED URANIUM AND 226RA IN THE MID-ATLANTIC COASTAL PLAIN: IMPLICATIONS FOR RADON HAZARDS

High concentrations of radon gas indoors is the second largest cause of lung cancer in the United States, following smoking. Identification of the geologic factors controlling radon risk is critical so that precautions can be taken to reduce radon concentrations in homes. The Atlantic Coastal Plain has a relatively high population density compared with other geologic provinces, but this region has not been studied extensively for radon hazards and is generalized as a low risk zone. A preliminary survey of radon gas concentrations in homes on the mid-Atlantic Coastal Plain of Virginia, however, indicates localized occurrences of up to 30 pCi radon activity per liter of air, which is over 10 times the U.S. Environmental Protection agency’s action level. We hypothesize that the Pliocene Yorktown Formation is the source of the high radon in the region, and test this by collecting core samples from 23 to 68 feet above sea level near Williamsburg, Virginia. We analyzed sediment for ²³⁸U, ²²⁶Ra, and ²¹⁰Pb activities using ultra low background high resolution gamma spectrometry and find that these radionuclides are very elevated near the base of the Yorktown, particularly in the coarse fraction (>2mm). Our measurements show that local ²²⁶Ra activities in bulk sediment exceed 300 Bq/kg, which is over 10 times the crustal average. High ²²⁶Ra/²¹⁰Pb indicates that more than half of the ²²²Rn gas emanates readily from this unit, and individual fossil vertebrae sections from sharks and whales are exceptionally high in uranium, up to 0.3 parts per thousand. We will study the mineralogical associations of the high uranium and radium sources to better document and predict the radon health hazards in this region.