Submitted to: Vadose Zone Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/14/2003
Publication Date: 11/3/2003
Citation: GAUR, A., HORTON, R., JAYNES, D.B., JACOBSON, L., AL-JABRI, S.A. USING SURFACE TIME DOMAIN REFLECTOMETRY MEASUREMENTS TO ESTIMATE SUBSURFACE CHEMICAL MOVEMENT. VADOSE ZONE JOURNAL. 2003. V. 2. P. 539-543. Interpretive Summary: Chemicals that leach through soil pose threats to surface and groundwater quality and human health. It is difficult and expensive to measure subsurface chemical movement and fate in soils. Computer models can be used to determine chemical fate and movement, but the soil properties needed to run the models are also difficult to measure. In this research, we demonstrated the potential benefits of a new technique for measuring chemical movement at the surface of soils. We also showed that the soil properties determined from these measurements could be used in a chemical fate and transport model to accurately predict the movement of chemicals deeper in the soil profile. These results will be of use to scientists and engineers interested in determining the fate and movement of chemicals applied to soils. Ultimately, the techniques developed here will be of use to regulators and others for regulating chemical use in the environment.
Technical Abstract: Chemicals that leach through soil pose threats to surface and groundwater quality. It is difficult and expensive to measure subsurface chemical transport and the transport properties required for extrapolating predictions beyond limited observations. The objective of our study was to evaluate whether solute transport properties measured at the soil surface could be used to predict subsurface chemical movement. The study was conducted in a greenhouse soil pit. The solute transport properties of the surface 2-cm soil layer were determined by using time domain reflectometry (TDR) to measure the bulk electrical conductivity during a step application of CaCl2 solution. The movement of chemicals in the subsurface was measured within the top 30 cm of soil following a pulse input of CaCl2 solution. A comparison of the measured chemical transport properties in the surface and subsurface zones of the soil showed that the parameters were similar. Furthermore, the estimated parameters determined by the surface TDR method were used to predict the chemical concentration distributions within the 30-cm soil layer, and it was found that the centers of mass of predicted chemical distributions were not significantly different from the measured ones. Therefore, the surface TDR measurements could be used to successfully predict subsurface chemical transport within the upper 30 cm of the soil. This surface measurement technique is a promising tool for vadose zone chemical transport studies.