In-situ characterization of soil-water content using gas-phase partitioning tracer tests: field-scale evaluation

Environ Sci Technol. 2003 Jul 15;37(14):3141-4. doi: 10.1021/es0340329.

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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Diffusion
  • Environmental Monitoring / methods*
  • Gases
  • Hydrocarbons, Fluorinated / analysis
  • Soil Pollutants / analysis*
  • Sulfur Hexafluoride / analysis
  • Volatilization
  • Water Pollutants / analysis*

Substances

  • Gases
  • Hydrocarbons, Fluorinated
  • Soil Pollutants
  • Water Pollutants
  • difluoromethane
  • Sulfur Hexafluoride