SORPTION OF ORGANIC VAPORS AT THE AIR-WATER-INTERFACE IN A SANDY AQUIFER MATERIAL

It was hypothesized that the mineral surfaces in a sandy aquifer material would be sufficiently hydrated in a GC column fed with humidified carrier gas to provide an air-water interface for the sorption of nonpolar organic vapors. To test this, the properties of three sorbents were investigated: an aquifer material, an oxidized version of the aquifer material, and a soil taken from the vadose zone overlying the aquifer. Isotherms, vapor-phase sorption constants, partial molar enthalpies of sorption, and the incremental free energy of sorption for a methylene group were measured using a variety of volatile organic compounds. The sorbents were also characterized with respect to specific surface area, organic carbon content, and water content. The sorptive properties of the oxidized aquifer material closely resembled those of water-coated silica, supporting the hypothesis. It was estimated that the air-water interface was responsible for up to 50 % of the observed sorption of alkanes in the aquifer material under the experimental conditions.