Determining transport parameters from laboratory and field tracer experiments

This bulletin describes a nonlinear least-squares inversion method that can be used to identify several parameters in a number of theoretical one-dimensional solute transport models. One of the models discussed is the usual convection-dispersion transport equation that includes terms accounting for linear equilibrium adsorption, zero-order production and/or first-order decay. In addition, a two-site/two-region model is described that can be applied to various non-equilibrium transport problems. Also included is a stochastic model that considers the effects of areal variations in hydraulic fluxes on field-scale solute transport. This last model also has provisions for zero- or first-order production and/or decay. The least-squares inversion method can be used to analyze both spatial and temporal distributions of flux or resident concentrations. A detailed description of the computer program, called CXTFIT, is given in one of the appendices of this bulletin. Several example problems illustrating practical applications of the program are discussed in detail.