Geologic Controls on Radon
Soil radon distribution in glaciated areas: An example from the New Jersey Highlands
Published:January 01, 1992
Alexander E. Gates, Lawrence Malizzi, John Driscoll, III, 1992. "Soil radon distribution in glaciated areas: An example from the New Jersey Highlands", Geologic Controls on Radon, Alexander E. Gates, Linda C. S. Gundersen
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In contrast to results of regional soil radon studies in unglaciated areas, bedrock geology shows no correlation with radon concentrations in glacial soils overlying the Green Pond outlier and Reservoir fault zone, New Jersey Highlands. Total gamma radiation and uranium concentrations in the Paleozoic sedimentary rocks of the Green Pond outlier are generally lower than in the Precambrian gneisses of the Reading Prong to the west. The sedimentary bedrock shows average gamma radiation of 220 c/s (136 to 323 c/s) and uranium concentrations of 0.5 to 0.6 ppm, whereas gamma radiation from the Grenville gneisses averages 284 c/s (240 to 576 c/s) and average uranium concentrations are 1.2 to 2.2 ppm. Rare pegmatites that occur along the Reservoir fault zone yield anomalously high average gamma radiation of 2,018 c/s (1,949 to 3,495 c/s) and average uranium concentrations of 28.5 ppm.
Radon concentrations in the glacial soil cover exhibited similar averages with wide ranges regardless of underlying bedrock geology. No appreciable difference was found between soil radon concentrations over Paleozoic sedimentary units, the pegmatites, fault zone, or Precambrian gneisses. Radon from soil over the Paleozoic sedimentary bedrock averaged 518 pCi/L (237 to 2,695 pCi/L), whereas it averaged 527 pCi/L (200 to 1,872 pCi/L) in soil over the Grenville gneisses.
The Green Pond outlier and the Reservoir fault zone are blanketed by the Wisconsin-age glacial cover and contain recessional deposits that are proximal to the terminal moraine. All soil radon was sampled in the glacial cover. The glacial sediments contain erratics primarily composed of lithologies in the area but also of exotic rock types. Because uranium concentrations in the erratics and matrix are highly variable, soil radon of individual samples is governed by the local uranium concentrations. Other possible reasons for the lack of correlation between bedrock and soil radon are the high permeability of the glacial soil that permits radon diffusion, atmospheric dilution, and variations in cover thickness.