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 hypothesis that the rate of desorption of a halogenated alkene from a water-saturated 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 environment. A batch desorption methodology (intermittent purging) was developed as an extension of a documented, long-term equilibration technique (flame-sealed ampules). A batch model incorporating radial pore diffusion with internal retardation captured the dynamics of the observed desorption behavior. However, the model consistently underestimated desorption rates at early times and overestimated rates at later times. The best-fitting effective pore diffusion coefficient values (D-p) for the Borden sand-fractions ranged over nearly 2 orders of magnitude (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.