COMPARISON OF INTRAPARTICLE SORPTION AND DESORPTION RATES FOR A HALOGENATED ALKENE IN A SANDY AQUIFER MATERIAL

The objectives of this research were 2-fold: (1) to test the hypothesi s that the rate of desorption of a halogenated alkene from a water-sat urated aquifer material equals the rate of sorption in that system and (2) to develop a technique for measuring desorption rates that would be useful in characterizing a large-scale, heterogeneous Subsurface en vironment. A batch desorption methodology (intermittent purging) was d eveloped as an extension of a documented, long-term equilibration tech nique (flame-sealed ampules). A batch model incorporating radial pore diffusion with internal retardation captured the dynamics of the obser ved desorption behavior. However, the model consistently underestimate d desorption rates at early times and overestimated rates at later tim es. The best-fitting effective pore diffusion coefficient values (D-p) for the Borden sand-fractions ranged over nearly 2 orders of magnitud e (7 X 10(-10) to 5 x 10(-8) cm(2)/s) and were, in most cases, two to four times lower than previous sorption rate estimates for the Borden sand. Possible reasons for the discrepancy are presented and discussed .