  In this work we investigate a coupled system of degenerate and nonlinear
partial differential equations governing the transport of reactive solutes in
groundwater. We show that the system admits a unique weak solution provided the
nonlinear adsorption isotherm associated with the reaction process satisfies
certain physically reasonable structural conditions. We conclude, moreover,
that the solute concentrations stay non-negative if the source term is
componentwise non-negative and investigate numerically the finite speed of
propagation of compactly supported initial concentrations, in a two-component
test case.
