An atomisitic etching model is combined with a continuum concentration solver in order to realistically simulate various effects during Deep Reactive Ion Etching (DRIE or the Bosch process). This includes microloading (or loading effect) and Aspect Ratio Dependent Etching (ARDE or lag effect). The model strongly differs from the current simulation approaches in which the local etch rate depends markedly on complex visibility integrals over the ion and neutral fluxes. Instead, we focus on the description of the etchant depletion.