A SIMPLIFIED WAVE-FORM ANALYSIS APPROACH FOR MONITORING SOLUTE TRANSPORT USING TIME-DOMAIN REFLECTOMETRY

Improved methods for monitoring transport of soluble chemicals in soil are needed for resolution of problems related to water quality. Our objectives were to simplify procedures associated with use of time-domain reflectometry (TDR) for monitoring soil solute transport, and to explore use of automated TDR for determining solute breakthrough curves under unsaturated steady flow conditions. A simplified method of waveform analysis was adapted for calculation of bulk soil electrical conductivity (sigma(a)), and applied to real-time measurement of solute breakthrough in an intact soil column. The technique utilizes ratiometric analysis of TDR waveform height at preincident step, prewaveguide, and ''final'' (several time constants beyond the transmission line terminus) waveform locations to calculate the resistive impedance load across a probe imbedded in soil. Transport of a Br- pulse through an intact soil column was monitored by this approach for a horizontally installed TDR waveguide. Results were compared with Br- concentration and electrical conductivity (sigma) of the effluent fractions. The breakthrough curve (BTC) based on sigma(a) was comparable to those using effluent analyses. Solute transport parameters (dispersion coefficient and retardation factor) estimated from the convective-dispersive equation for the sigma(a) BTC were not different from those derived from effluent cr and effluent Br- BTCs. This measurement approach may be easily incorporated into existing computer- and datalogger-controlled acquisition and analysis systems, and provides improved ease of use, accuracy, and flexibility for investigation of chemical transport in soils.