The detoxification of liquid contaminants in a porous medium is numerically investigated by solving the conservation equations of mass, momentum and chemical concentration in the internal and external regions of the porous medium. A level-set formulation for two-phase flows is extended to include the effects of porosity and mass transfer with chemical reaction. The numerical computations demonstrated the effects of droplet size, impact velocity, initial concentration, porosity and chemical rate constant on the remaining mass of liquid contaminant. The time variation of the concentration field and remaining mass of liquid contaminant is distinguished between the very short initial period, when the droplet impact driven flow is dominant, and the later period, when the diffusion effect is dominant in the completely absorbed droplet.