Fig. 5. Twenty-one day naphthalene adsorption isotherm for Lerbjerg sandy clay (L5) and subsequent 2 d desorption steps. The adsorption is approximated by a linear isotherm . A linear isotherm is plotted for the first and the last desorption step corresponding to an apparent K_D value between 13 cm³ g^-1 and 93 cm³ g^-1 for contact times (adsorption plus desorption time) between 552 and 1080 h.