Alluvial aquifer samples from the same depth but different locations and from different depths at the same location were characterized and evaluated both for the nature of their organic matter and their sorption properties. Both equilibrium and kinetic sorption were evaluated using batch studies with phenanthrene. Organic petrology was used both qualitatively and quantitatively to explain and predict the patterns of sorption for each sample. Organic carbon content values varied by 1 order of magnitude, and sorption capacities varied by 2 orders of magnitude within a given depth and location for these samples. The sorption isotherms ranged from nonlinear to virtually linear. The organic content-normalized distribution coefficients (K{sub}(OC)) varied significantly between organic matter subgroups as did the time to reach equilibrium. We were able to correlate these variations in sorption behavior with the organic matter type in subgroups. K{sub}(OC) values were assigned to each organic matter subgroup and were used along with the fraction of each organic matter subgroup to predict the composite K{sub}(OC) values. Close agreement between predicted and measured K{sub}(OC) values validated this approach. Using the subgroup K{sub}(OC) values and literature fraction organic carbon (f{sub}(OC)) values, the sorption distribution coefficients were also predicted within the 95 confidence intervals for the measured values. Our results also demonstrate that opaque organic matter fractions dominate the sorption process and that quantifying this fraction alone can virtually predict the sample K{sub}(OC) value.
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