Organic Carbon Dominated Trichloroethene Sorption in a Clay‐Rich Glacial Deposit

Abstract

AbstractThe relative contributions of organic carbon and mineral matter to trichloroethene (TCE) sorption were determined for a natural, clay‐rich till from Sarnia, Ont. using laboratory batch tests. Linear TCE sorption coefficients of the two till samples (approximataely 12 to 15 m depth) were 64.2 l/kg and 151 l/kg and the organic carbon contents (foc) were 0.68% and 1.95%, respectively. To ascertain the importance of sorption to mineral matter versus organic carbon, till samples were treated by baking. The foc was reduced by 44 to 90% in treated samples compared to natural samples. TCE sorption coefficients were also reduced to 0.48 to 4.64 l/kg in treated samples. Surface area measurements suggested that treating the till samples appeared to have little effect on the mineral matter. The results indicated that TCE sorption is dominated by the naturally occurring organic carbon. The organic carbon normalized sorption coefficients (Koc) for the natural (untreated) samples were 16 to 500 times greater than those typically reported for sediment and soil samples, indicating the more lipophilic character of the organic matter in the till. Koc estimates which accounted for the oxidation state of the organic carbon in the till assuming the carbon is primarily from Devonian‐age shale fragments resulted in values close to (within a factor of 2 to 5) those observed. Thus, both the nature and amount of organic carbon in the till play major roles in controlling the magnitude of TCE sorption in this clay‐rich deposit.