ABSTRACT
The predictability of radon production from bedrock is anticipated by a combination of uranium endowment and distribution of uranium into mineral phases. Olszewski and Boudette have synthesized a map of New England at 1:1,000,000-scale which shows 11 rock units. These units are discriminated by geologic factors including measured uranium distribution. The average uranium content varies from very low (< 1 ppm) to very high (> 29 ppm). Uranium in rocks and in soils derived from a rock and radon in air and ground water in the environment should show a direct correlation in most instances. This observation has been borne out by information assembled from air and water sampling particularly in Maine and New Hampshire. Other controls that influence radon production relate to mobility of uranium in ground water. Transport can led to a secondary enrichment of uranium (or radium) which contributes to local high levels of radon. Two-mica granite provides an excellent example because the uranium is nearly all labile, and high radon values occur in ground water associated either with pegmatite or deposits of secondary uranium minerals. Alkalic or calc-alkalic granite is also high in uranium, but it tends to be stabilized within accessory minerals. Thus, the radon levels associated with these rocks are not as high as in two-mica granite. Hydrologic 16response to a pumping well also has a role in determining radon content of well water. Altering geochemical conditions in the flow field and aquifer stress providing increased rates of radon transport with induced ground-water flow appear to be the primary controls.
