[en] Sweden received a particularly high level of fallout from the reactor accident at Chernobyl in April 1986. An environmental monitoring programme was initiated jointly by the CEGB and Studsvik to study the behaviour of the deposited radionuclides in the rural and urban environment of Gaevle where the highest depositions were recorded. This report is concerned with the analysis of the rural data collected over the period from August 1987 to August 1988. The aim has been to develop an improved model to predict the migration of radionuclides through pasture soil. Two alternative models were developed; the first a compartment model and the second a diffusion-advection model modified to account for fixation. The predictions of the two models were tested against the results of the monitoring programme. Least squares analyses were used to establish the better of the two models and to obtain estimates of the model parameters. In all but one case, the diffusion model was found to provide the better description of the behaviour of radionuclides; the effect of advection was found to be negligible. It is intended that this model will be incorporated into an improved model to predict the uptake of activity into animal products. (author)