title: In-situ characterization of soil-water content using gas-phase partitioning tracer tests: field-scale evaluation.
abstract: Field-scale tests were performed to evaluate the effectiveness of the gas-phase partitioning tracer method for in-situ measurement of soil-water content. The tracer tests were conducted before and after a controlled infiltration event to evaluate performance at two water contents. Nonpartitioning (sulfur hexafluoride) and water-partitioning (difluoromethane) tracers were injected into the test zone, and their effluent breakthrough curves were analyzed using the method of moments to calculate retardation factors for difluoromethane. Soil-water contents estimated using the tracer data were compared to soil-water contents obtained independently using gravimetric core analysis, neutron scattering, and bore-hole ground penetrating radar. For the test conducted under drier soil conditions, the soil-water content estimated from the tracer test was identical to the independently measured values of 8.6% (equivalent to water saturation of 23%). For the test conducted under wetter soil conditions, the tracer test derived soil-water content was 81% of the independently measured values of 12.2% (equivalent to water saturation of 32%). The reduced efficacy at the higher soil-water content may reflectthe impact of advective and/ or diffusive mass transfer constraints on gas-phase transport. The results presented herein indicate that the partitioning tracer method is an effective technique to measure soil-water content at the field scale, especially for sites with moderate to low soil-water contents.
authors.affiliation: Department of Soil, Water, & Environmental Science, The University of Arizona, 429 Shantz Building, Tucson, Arizona 85721, USA.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Keller
authors.forename: Mark L
authors.initials: ML
authors.lastname: Brusseau
mesh_terms: D004058:Diffusion; D004784:Environmental Monitoring / Q000379:methods*; D005740:Gases; D006845:Hydrocarbons, Fluorinated / Q000032:analysis; D012989:Soil Pollutants / Q000032:analysis*; D013459:Sulfur Hexafluoride / Q000032:analysis; D014835:Volatilization; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D005740:Gases; D006845:Hydrocarbons, Fluorinated; D012989:Soil Pollutants; D014873:Water Pollutants; C102075:difluoromethane; D013459:Sulfur Hexafluoride