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The application of the general advection-diffusion equation to model evaporatively-driven, groundwater flux rates from solute concentration soil profiles was developed in the 1980's and has been applied to a variety of arid zone locations, including salt lakes, valley floors and discharge zones of regional groundwater. In this paper we revisit and extend the model by accounting for the effects of variable water content and sediment type on the impedance factor, and in turn, effective diffusion coefficient. We also explore the sensitivity of the extended model to its major assumptions and parameter values. Early studies typically used a Penman tortuosity value of 0.66 to account for the impedance factor. In this study, we apply the constant slope impedance factor (CSIF) method to calculate the impedance factor relating the effective diffusion coefficient to the self-diffusion coefficient of the tracer and water content, from soil textural properties. The threshold water content is the water content at which flow paths become discontinuous and varies with soil type (e. g. gravel<0.04, sand<0.13, silt<0.21, clay<0.32 v/v). Relative to the Penman tortuosity value previously used, the CSIF method resulted in reductions in the mean effective diffusion rates of between 70-96% in field soil chloride profiles. The mean diffusion coefficient of the soil profile data used in the advection-diffusion model is dependant on the boundary conditions that set the length of the profile, particularly on the position of the evaporation front. In field soil profiles, there can be some uncertainty in the position of the evaporation front based upon the use of different solutes (e. g. chloride and delta O-18) that result in considerable variation in the mean diffusion coefficient for the profile. The CSIF method for calculating the mean diffusion coefficient is very sensitive to the volumetric water content of the profile, particularly at the top of the profile close to the evaporation front. The effective depth function results in samples substantially drier than lower samples having a large influence on the mean effective diffusion coefficient of the profile and hence on the modelled evaporation rates. The uncertainty in the position of the groundwater reservoir and its concentration has little effect where the lower part of the profile shows an asymptotic trend towards a representative value of groundwater concentration but can vary substantially with different values of groundwater depth and concentration if this is not the case.