| Chlorinated solvents such as tetrachloroethylene (PCE), trichloroethylene (TCE) and 1,1,1-trichloroethane (1,1,1-TCA) have been widely used in the dry-cleaning industry and as metal degreasing solvents. As a result of widespread use and accidental releases (vapor, leakage, wastewater discharge and combustion, etc) into air, soil and groundwater over the last decades, high concentrations of chlorinated solvents are frequently found in soil and groundwater in the industrialized world. Sorption affects the stored mass of contaminant, the effective rate of diffusion and thereby the mass transfer of contaminants between the sorbed phases on the matrix solids to the mobile aqueous phase in the fractures. Thus, sorption plays an important role in transport and fate of chlorinated solvents during remediation process. There are few previous studies focused on the sorption of PCE and TCE on clayey tills, and correspondingly higher sorption capacity was observed than expected, However, the sorption of cis-dichloroethylene(cis-DCE) and vinyle chloride (VC), as well as 1,1,1-TCA, 1,1,-dichloroethane (1,1-DCA), and chloroethane (CA) on natural clayey till has not previously been reported. In addition, the pore size distribution (PSD) has an impact on the migration and growth of dechlorinating bacteria in clayey till matrix, affecting the efficiency of contact and mixing of electron donor, dechlorinating bacteria and chlorinated comtaminants, thereby controlling the timeframe and removal rate of chlorinated solvents by ERD. However, the information with respect to the distribution of dechlorinating bacteria between clayey till matrix and fracture apertures and the effect of PSD in clayey tills on the growth and migration of dechlorinating bacteria have not been previously reported.The geological, hydrogeological characterization, deposition history and physical and chemical properties of clayey tills in Danish contaminated field sites were carried out by field investigation and reference data, providing background information for discussion. The results showed that all investigated clayey tills were classified as basal tills. The clayey tills from Vadsbyvej site were deposited during the late Weichselian glaciation and originate from the Baltic region. During several ice advances till units with different characteristics were deposited all over the eastern part of Denmark. The H?je Taastrup vej site is located in the same regional geological setting as the Vasbyvej site. The geology at the Rug?rdsvej site was formed during the Weichsel Ice age. Regional geologic profiles suggest the upper sediments were deposited during varying progressions of the glacier and ice melt-off events. Furthermore, the specific surface area (SSA) of all clayey till samples was 10-14 m2/g, which related well with clay content of clayey till samples. The clay mineralogy of all clayey till samples was similar, mainly composed of quartz, calcite, feldspar and minor clayey mineral. The clay content of clayey till samples ranged from 23% to 27% and organic carbon fraction (foc) of clayey till samples was lower than 0.1%, ranged from 0.02% to 0.08%.Then, the sorption of chlorinated solvents and degradation products on 7 natural clayey till samples from 3 contaminated sites was investigated by laboratory batch experiments in order to obtain reliable sorption coefficients (Kd values). The results showed that equilibrium time of chlorinated solvents and their degradation products are 3 day. From a practical point of view, linear isotherm is superior to the Freundlich isotherm. For chloroethylenes, PCE was most strongly sorbed to the clayey till samples (Kd = 0.84-2.45 L/kg), followed by TCE (Kd = 0.62-0.96 L/kg), cis-DCE (Kd = 0.17-0.82 L/kg) and VC (Kd = 0.12-0.36 L/kg). For chloroethanes, 1,1,1-TCA was most strongly sorbed (Kd = 0.2-0.45 L/kg), followed by 1,1-DCA (Kd = 0.16-0.24 L/kg) and CA (Kd = 0.12-0.18 L/kg). This is consistent with the order of hydrophobicity of the compounds. Moreover, the estimated logKoc or logKd 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. Multiple regression analysis of the relationships between Kd, SSA, foc and clay content was performed for samples with data on chloroethylenes. The analysis indicates that the Kd values of chlorinated solvents and degradation products are not only dependent on foc, but also other factors like clay content may be at least as important for the sorption on natural clayey till samples with foc lower than 0.1%.Abdul's empirical relationship and the logKd-logKow and logKoc-logKow relationships from this study were applied to the dataset from Rug?rdsvej site. The results indicated that Abdul's relationship clearly underestimates the sorption capacity of cis-DCE and VC. The logKd-logKow and logKoc-logKow relationships from this study result in much better comparison of both concentration and composition of contaminants with groundwater data than Abdul's relationship or any of the other previous empirical relationships, though as expected they do not provide as good a comparison as use of the site specific Kd values. Therefore, for complete site evaluation purposes, the logKd-logKow relationship developed based on 3 clayey till sites and more clayey till units/conditions may be more appropriate to use than a single site specific Kd value, provided site specific Kd values (for one or more of the compounds) falls or based on depository history and foc can be expected to fall within/near the range observed in this study.Finally, the pore structure and pore size distribution (PSD) were investigated by back-scatter electron microscope and Image J software analysis, then the effect of PSD on growth and migration of dechlorinating bacteria was evaluated. The results illustrated that the pore structure and pore size of clayey till samples varied at different field sites. The macroporosity of Vadsbyvej, Gl. Kongevej and Sortebrovej site determined by image analysis were in a range of 6%-14%, 6%-12% and 6%-16%, respectively, which were less than half of the total porosity determined from lab measurements. The typical macropore sizes of all investigated clayey till samples were ranged from 1μm to 10μm. In conclusion, it is found that macropores corresponding to approximately 30%-50% of total porosity have diameters between 1-100μm in clayey till samples, which significantly differs from the data of pore sizes of clayey soils and other deposits (0.01-0.3μm) in literatures. Besides, the fracture aperture determined by image analysis was less than 50μm, in the range of the data (1-100μm) from the literatures. It is tentatively proposed that macropores in clayey till samples were not inner-connected well in 3 dimension. There was a positive correlation between macroporosity and clay content of clayey till samples (R2=0.91), while a negative correlation between macroporosity and SSA (R2=0.53) and D50 (R2=0.35).Recently, at least 18 dechlorinating bacteria have been isolated and identified as Desulfitobacterium sp., Sulfurospirillum sp., Desulfomonile sp., Desulfuromonas sp., Geobacter sp., Dehalococcoides sp. and Dehalobacter sp. The typical shapes of them are rod, coccoid or disc shaped and typical size ranged at 0.3-1μm. In particular, the dechlorinating culture KB1 was coccoid, and the dominated size was less than 1μm.The macroporosity data determined in this study were compared with the dataset of dechlorinating degree collected after 1556 days'injection of culture KB1? from Sortebrovej site. It can be found that the macroporosity data were integrated well with the dataset of dechlorinating degree from field site, illustrating the effects of PSD on growth and migration of dechlorinating bacteria through clayey till matrix. The macropores, approximately 50% of total porosity determined by lab measurement in this study, may provide a good channel/space for dechlorinating bacteria to migrate from high permeability like fracture/sand lense to low permeable clayey till matrix. In conclusion, the migration of dechlorinating bacteria from fracture aperture (or hydraulic induced)/sand lense to clayey till matrix may exist and thereby the growth and colony of dechlorinating bacteria within macropores or fractures are likely occurred, if injected electron donor and other nutrients are enough for bacteria's activity.
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