  In this work we consider the transport of a surfactant in a variably
saturated porous media. The water flow is modelled by the Richards equations
and it is fully coupled with the transport equation for the surfactant. Three
linearization techniques are discussed: the Newton method, the modified Picard
and the L-scheme. Based on these, monolithic and splitting schemes are proposed
and their convergence is analyzed. The performance of these schemes is
illustrated on four numerical examples. For these examples, the number of
iterations and the condition numbers of the linear systems emerging in each
iteration are presented.
