This paper proposes a tower-foot grounding system model compatible with EMT programs which might be useful for the simulation of lightning transients in overhead lines. The proposed model is based on the solution of the telegrapher's equations and the application of the classical Marti's transmission line model. The model is implemented in the Alternative Transients Program (ATP) and validated considering a benchmark electromag-netic model. Its accuracy is evaluated and shown both in terms of the simulated ground potential rise (GPR) and line overvoltages developed through the insulator strings due to lightning currents. Finally, the model accuracy is also demonstrated in terms of the line backflashover outage rate.