TRITIUM AND HELIUM-ISOTOPES AS HYDROLOGIC TRACERS IN A SHALLOW UNCONFINED AQUIFER

Measurements of tritium and 3He in groundwater can be used to calculate the age of tritium in groundwater. Such combined measurements on water samples thus provide a powerful tool towards understanding fluid flow in the near-surface saturated zone. The authors report tritium and helium isotope measurements on waters from an unconfined aquifer associated with a low-level nuclear waste storage area. These values are used to calculate ages of tritium in groundwater from 0.1 to 6 years. From the groundwater ages and a three-dimensional flow net hydraulic conductivities of 3.3×10-6 to 5.5×10-6 m s-1 for five wells, and extreme values from a single well of 18×10-6 and 97×10-6 m s-1, are calculated. These values agree with hydraulic conductivities obtained from conventional aquifer tests. The high conductivity value may indicate an area of preferred fluid flow.