Sorption of chlorinated solvents and degradation products on natural clayey tills.

The sorption of chlorinated solvents and degradation products on seven natural clayey till samples from three contaminated sites was investigated by laboratory batch experiments in order to obtain reliable sorption coefficients (K(d) values). The sorption isotherms for all compounds were nearly linear, but fitted by Freundlich isotherms slightly better over the entire concentration range. For chloroethylenes, tetrachloroethylene (PCE) was most strongly sorbed to the clayey till samples (K(d)=0.84-2.45Lkg(-1)), followed by trichloroethylene (TCE, K(d)=0.62-0.96Lkg(-1)), cis-dichloroethylene (cis-DCE, K(d)=0.17-0.82Lkg(-1)) and vinyl chloride (VC, K(d)=0.12-0.36Lkg(-1)). For chloroethanes, 1,1,1-trichloroethane (1,1,1-TCA) was most strongly sorbed (K(d)=0.2-0.45Lkg(-1)), followed by 1,1-dichloroethane (1,1-DCA, K(d)=0.16-0.24Lkg(-1)) and chloroethane (CA, K(d)=0.12-0.18Lkg(-1)). This is consistent with the order of hydrophobicity of the compounds. The octanol-water coefficient (logK(ow)) correlated slightly better with logK(d) values than logK(oc) values indicating that the K(d) values may be independent of the actual organic carbon content (f(oc)). The estimated logK(oc) or logK(d) for chlorinated solvents and degradation products determined by regression of data in this study were significantly higher than values determined by previously published empirical relationships. The site specific K(d) values as well as the new empirical relationship compared well with calculations on water and soil core concentration for cis-DCE and VC from the Rugårdsvej site. In conclusion, this study with a wide range of chlorinated ethenes and ethanes--in line with previous studies on PCE and TCE--suggest that sorption in clayey tills could be higher than typically expected.