AQUATIC-TERRESTRIAL PARTITIONING OF DEEP GROUNDWATER DISCHARGE USING MEASURED HELIUM FLUXES

Performance assessments of nuclear fuel disposal vaults deep in the ge osphere have generally assumed that all deep groundwater enters a lake or river and that no wetland or terrestrial discharge occurs. Animal licks in Ontario and Alberta, Canada, indicate that saline waters typi cal of deep groundwater do emerge in the biosphere. Helium gas, produc ed in situ in granitic rock, is used in this study to partition ground water discharge. He flux comparisons were made on a flood plain with a nomalously high He concentrations in the surface water of a creek and in the soil gas of an adjacent deer lick. This unique study, comparing direct flux-chamber methods with indirect methods using ping-pong bal ls as He gas collectors, indicates that 92% of the He produced in situ in the granite below this flood plain enters the creek and 8% enters the wetland. This partitioning is sensitive to the size of the terrest rial are a considered and could be as high as 83% aquatic and 17% terr estrial at this location. Although this represents only one site, it s uggests biosphere assessment models could use an aquatic-terrestrial p artition of up to 80/20 for deep groundwater discharge unless site-spe cific data are available.