The long-term objective of this project is to enable us to predict the relevant sorption equilibrium or kinetics for toxic organic compounds present in groundwater environments. Such predictions are necessary, not only to estimate the hazard posed to people living near buried organic wastes and using the surface and subsurface waters polluted by these chemicals, but also to evaluate many clean-up strategies which rely on compound desorption to enable (bio)degradation or removal in pumped water or soil air. The experimental design involves first establishing an equilibrium description for real world subsurface solids acting as sorbents, and then tackling the kinetics problem by identifying the slowest solid-water exchange step beginning at the grain scale and working up to larger and larger scales. First, we hypothesize that nonpolar compound sorption to subsurface minerals (with very low organic contents) involves dissolution in """"""""vicinal"""""""" waters filling the solid-phase micropores. By examining the correlation of microporosity and sorptive equilibrium coefficients, we hope to demonstrate the validity of this hypothesis. Next, we speculate that long-term sorptive exchange is limited by the rate of transfer of sorbate molecules into the microporous space of larger grains. We will seek to relate the volume of microporous space and the magnitude of K(D) to the observed rates of uptake and release of sorbates like trichloroethylene. This will help us ascertain the controlling sorption mechanism(s). To gauge the importance of such grain-scale kinetics, we will compare the observed rates with those we see from a set of flow- interrupt breakthrough experiments relying on short, but intact, soil cores drawn from sites within the Aberjona Basin.
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