WRRCSR No.06:01:90 Injected Helium: A New Hydrological Tracer

Abstract

Five types of experiments were conducted to investigate dissolved helium gas as an injected water tracer, both in the subsurface water and open water: instrument development, sand column, soil columns, groundwater in basalt aquifer, and open water in tank and flume. Thirty-four Board of Water Supply pumping wells were sampled and 7 USGS wells were utilized. Much subsurface water data were simulated by transport models. The project developed a helium-detection system which consists of a thin quartz-glass membrane and a diode-ion pump. The system responded linearly to helium diffusion through the membrane over a range of six orders of magnitude. The test results demonstrated that helium is an ideal water tracer for groundwater in the saturated zone because of the attributes of helium: conservative nature, easy to use, low cost, absence in nearly all natural water, safety to the environment and humans. For the unsaturated-zone tests, exchange of helium with air entrained in the porous media reduced the usefulness of helium. In the open-water tests, helium behaved like fluorescein in a relatively tranquil submerged environment for hours but was gradually lost through air-water interface, thus limiting the usefulness of helium to short-duration studies or in a submerged environment.