Development of a New Technique for the Use of Dissolved Helium as an Environmental Groundwater Tracer

Development of a New Technique for the Use of Dissolved Helium as an Environmental Groundwater Tracer

National Institute for Water Resources, Water Resources Research Institute Program

3/1/2005 - 2/28/2006

Tracer tests are an important method for determining the flow characteristics and patterns of subsurface water (such as groundwater aquifers) and surface water bodies (such as streams and the ocean). In such tests, a constituent is added to the water. The constituent is either non-native to that water or high enough in concentration to be distinguished from the native component in that water. Many of the commonly used tracers have one or more limitations, such as being toxic, being esthetically objectionable, being difficult to be differentiated from the naturally occurring fraction, requiring complex laboratory analysis for their detection and quantification, requiring a high concentration, and reacting with the aquifer matrix. These limitations are not common to helium, however. Thus, if a field method can be developed to detect and quantify the concentration of dissolved helium in surface or groundwater in real time, then helium has great potential for use in certain tracer applications, including its use near drinking water sources or in environmentally sensitive areas such as wetlands and fish farms, its use in areas where esthetics are a concern (e.g., recreational beaches), and its use in conjunction with investigations of the diffusion characteristics of groundwater aquifers.

Helium was successfully tested as a reliable and economical tracer (S.K. Gupta, L.S. Lau, P.S. Moravcik, and A.I. El-Kadi, 1991, Injected Helium: A New Hydrological Tracer, Special Report 06.01.90, Water Resources Research Center, University of Hawaii at Manoa, 94 pp.; L.S. Lau, and P.S. Moravcik, 1994, Ground-Water Tracing with Injected Helium, Ground Water 32(1):96–102). Its behavior in open tanks was identical to that of fluorescein dye. Although the system was simple and specific for helium, the small surface area and fragility of the thin quartz window limited its sensitivity and reliability. Moreover, the technique was only suitable for the analysis of discrete samples.

The objective of this project was to develop and demonstrate a new analytical system that substantially improves the precision and utility of the helium tracer for routine use in surface water and groundwater. The work encompasses developing and calibrating the system, and testing the helium tracer in the laboratory against a commonly used tracer.

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