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 o bjectives were to simplify procedures associated with use of time-doma in reflectometry (TDR) for monitoring soil solute transport, and to ex plore use of automated TDR for determining solute breakthrough curves under unsaturated steady flow conditions. A simplified method of wavef orm analysis was adapted for calculation of bulk soil electrical condu ctivity (sigma(a)), and applied to real-time measurement of solute bre akthrough in an intact soil column. The technique utilizes ratiometric analysis of TDR waveform height at preincident step, prewaveguide, an d ''final'' (several time constants beyond the transmission line termi nus) waveform locations to calculate the resistive impedance load acro ss a probe imbedded in soil. Transport of a Br- pulse through an intac t soil column was monitored by this approach for a horizontally instal led TDR waveguide. Results were compared with Br- concentration and el ectrical conductivity (sigma) of the effluent fractions. The breakthro ugh curve (BTC) based on sigma(a) was comparable to those using efflue nt analyses. Solute transport parameters (dispersion coefficient and r etardation factor) estimated from the convective-dispersive equation f or the sigma(a) BTC were not different from those derived from effluen t cr and effluent Br- BTCs. This measurement approach may be easily in corporated into existing computer- and datalogger-controlled acquisiti on and analysis systems, and provides improved ease of use, accuracy, and flexibility for investigation of chemical transport in soils.