A compartmental screening model was developed to describe the movement of volatile and transformable organic chemicals in rapid-infiltration wastewater treatment systems. The first compartment describes losses of the chemical from the infiltration basin when the basin is flooded with wastewater. The second compartment considers losses due to volatilization and transformation in near surface soils during periods of drying. The third compartment describes the transport and transformation of the remaining chemical to ground water. The model was developed to consider an accidental spill of chemical into a treatment system or a constant input of chemical into a system. No attempt was made in this investigation to evaluate the model's suitability for describing an accidental spill into a treatment system. Projections of volatilization were within a factor of 2 for slowly transformable compounds. The model overestimates volatilization for degradable compounds if one assumes no transformation.