The dispersion of a pollutant solution in a flow through a porous medium was investigated. A theoretical solution was obtained for the general, two-dimensional, convective-dispersion equation that describes the dispersion of a miscible, second fluid through a seepage flow. Application of the theoretical results requires knowledge of the basic seepage flow, the pollutant (second fluid) source concentration, and the longitudinal and lateral dispersion coefficients of the porous medium. A simplified theory and experiments were conducted to determine the coefficients. Their values found in the present study are in agreement with previously published results. Theoretical and experimental breakthrough curves for the general theory are presented and appropriate comparisons made. The unsteady growth of the dispersion front is shown, and the significant effects of both the longitudinal and lateral dispersion phenomena are clearly demonstrated.