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Radon survey techniques are being used to determine whether significant variations of Rn222 content occur in soil gases of northeastern Ohio and, if so, whether they have hydrocarbon prospecting potential. Radon activities are determined by using electronic detectors for short-term variations and film cups for long-term variations.
Preliminary traverses covered more than 300 sites. Three localities were found in which the radon activities are reproducibly higher than regional "background" by a factor of 5 to 10. One case correlates with proximity to the outcrop belt of the uranium-rich Huron Member of Ohio Shale. The others consist of localized anomalies not directly associated with uranium-rich shales. Laboratory experiments of soil samples showed radon in anomalous regions is not produced in situ within the upper 1 to 2 ft (0.3 to 0.6 m) of soil, suggesting a deeper origin for migration of radon to near-surface soil gas.
Occasional localized seeps of natural gas occur in northeastern Ohio. Light hydrocarbons C1 to C3 are usually associated with reducing environments causing precipitation of uranium and its products at shallow depths which could conceivably enhance radon activity at the surface. Also, hydrocarbons migrating upward from deeper sources would carry radon to the surface along more permeable and fractured rocks and create a radon anomaly. Light hydrocarbon analyses of shallow soil gases showed greater total hydrocarbon contents and greater C2/C1 and C2/C3 ratios in areas of higher radon activities. Measurements of hydrocarbons at greater soil depth, coupled with additional radon measurements, are in progress to interpret furt er the significance of radon-survey data.
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