Analysis of partial breakthrough data by a transfer-function method

Abstract

A transfer-function method has been applied to determine solute-transport parameters from earlier sections of complete breakthrough data. Time-domain reflectometry allows the measurement of breakthrough data in unsaturated soil. In fine-textured soils, the flow of water must be kept low to maintain unsaturated conditions, and so experiments for a complete breakthrough of solute may last a very long time. Substantial savings of time and computer memory might be achieved if data could be analysed from an earlier section of breakthrough data. Data at 2 vertical positions (input at upper and response at lower position) from a complete breakthrough of calcium chloride applied as a pulse input to 4 unsaturated soils (coarse sand, sandy loam, clay loam, clay) were divided into 4 sets of increasing duration. Transport parameters of calcium chloride were determined by a transfer function, which results in similar values of the parameters from the last 3 datasets in all 4 soils. In the clay soil, however, because of erroneous breakthrough data the fit between the measured and estimated breakthrough curves (BTCs) was poor, but the transport parameters were consistent among different segments of data. We show that it is possible to determine successfully solute-transport parameters from partial breakthrough data, which include the peak of the response BTC. This transfer-function method is thus a powerful tool to shorten breakthrough experiments.