Intermediate-scale tests of the gas-phase partitioning tracer method for measuring soil-water content

Experiments were conducted in a well-instrumented weighing lysimeter (2.5 by 4 m) to evaluate the efficacy of the gas-phase-partitioning tracer method for measuring soil-water content. The method is based on the use of conservative (nonpartitioning) and water-partitioning tracers, wherein the partitioning tracer transfers into the water, which retards its movement with respect to that of the nonpartitioning tracer. This retardation is a function of the soil-water content. The volumetric soil-water contents estimated from comparative moment analysis of the measured breakthrough curves were compared with values obtained using traditional methods, including gravimetric core analysis, neutron thermalization, time domain reflectometry, and conversion of soil tension. The values obtained from the tracer tests compare favorably with the independently determined values. For the lower soil-water contents (6-7%), the tracer-estimated values were ≈98% of the measured values. For the higher soil-water content (15%), the tracer estimated values were ≈77% of the measured values. These results indicate that the gas-phase partitioning tracer method can provide representative estimates of soil-water content under the relatively ideal conditions employed herein.