THE IMPACT OF SORPTION MECHANISM ON CHLORINATED SOLVENT UPTAKE RATE VIA INTRAGRANULAR DIFFUSION IN KEROGEN-CONTAINING SEDIMENTARY ROCK GRAINS

We posit that one cause of chlorinated solvent persistence in sedimentary aquifers is mass storage within ‘high sorbing’ porous grains. Herein, mass uptake and release are limited by intragranular diffusion enhanced by intragranular sorption to carbonaceous matter. Previous studies demonstrated that the dominant mechanism of organic contaminant sorption is different at high and low concentrations when sorption is nonlinear with respect to concentration. The objective of this study is to determine whether sorption mechanism affects the rate of contaminant uptake by sedimentary rock grains containing kerogen sorbent. The approach uses high- and low-trichloroethene (TCE) concentration experiment pairs to isolate the dominant sorption mechanism; high~25% TCE solubility and low~0.1%. In this investigation, carbonate grains from the Gull River Formations of Ontario, Canada are amended with TCE and sampled over time to track contaminant uptake. Grains of uniform size are prepared from outcrop samples, with weathered portions removed. Nonlinear intragranular diffusion simulations incorporating the parameters of the contaminant and the sediments used in the experiments will serve as a standard for comparison with the experiment results and to distinguish processes. Important parameters for the simulation obtained from prior laboratory experiments are sorption isotherm parameters and porosity. Plots of contaminant mass distribution among phases over time are expected to show differences in uptake rates between the high- and low- concentrations that are not explained by the difference in driving force alone and indicate that the concentration dependent sorption mechanism affects uptake rate.