In the Bitterfeld lignite seam aquitard we have observed asymmetric Gaussian-like concentration profiles of organic contaminants. Similar concentration profiles were observed in a clayey groundwater aquitard at Dover Air Force Base, Delaware. For a diffusion-based interpretation of these concentration profiles Ball et al. (1997) have derived an analytical solution for the two-aquitard diffusion problem. Applying this general solution, we derived for the first time an analytical expression for the contaminant release function /(f). The knowledge of this function is necessary both for forensic modelling of the case history and for predictive modelling of the future contaminant release of the aquitard.