Helium accumulation in groundwater. II: A model for the accumulation of the crustal 4He degassing flux

A model of ⁴He accumulation in a confined aquifer is presented which includes in situ production and a crustal degassing flux of ⁴He into the bottom of a confined aquifer. The model is consistent with the measurements of ⁴He concentration in the Great Artesian Basin, Australia (Torgersen and Clarke, 1985) and also with the measurements of ⁴He concentration in the Auob Sandstone of Namibia (Heaton, 1981). The measured value of the crustal degassing flux of ⁴He from these two areas is comparable with the ⁴He degassing flux calculated from the atmospheric budget of ⁴He (Wasserburget al., 1963; Ozima and Podosek, 1983). A literature review suggests that a crustal degassing ⁴He source may account for the ⁴He accumulation in many other groundwater systems. It is concluded from the literature review, the detailed modelling of ⁴He accumulation in GAB and the Auob Sandstone, and the atmospheric budget that crustal degassing of ⁴He may be a common and widespread phenomena.