Fig. 3. Measurement of specific air–water interfacial areas (a_i). (a) Breakthrough curves (BTCs) for methane and n-hexane at different water contents (_w). The pore volume scale is the total volume of column effluent after volatile organic compound (VOC) introduction divided by the gas volume in the column, and the term C_g is the concentration normalized by the total area of the BTC. (b) Measured mean total retardation factor (R_t) values for n-hexane and calculated a_i values.