Field Evaluation of Biological Enhanced Reductive Dechlorination of Chloroethenes in Clayey Till

Abstract

The performance of enhanced reductive dechlorination (ERD) for in situ remediation of cis-1,2-dichloroethene (cDCE) and vinyl chloride in clayey till was investigated in a pilot test. A dilute groundwater solution containing emulsified soybean oil and Dehalococcoides bacteria was injected into a sand-filled hydraulic fracture. Fermentation of the ERD solution caused the establishment of a dechlorinating bioactive zone in the fracture within 1 month of injection. By 148 days, all the cDCE in the fracture was dechlorinated to ethene. Analysis of a clay core from Day 150 indicated that electron donor and fermentation products diffused from the fracture at least 10 cm into clay and that stimulated dechlorination occurred in the clay in the presence of Dehalococcoides (7.9.10(4) cells g(-1)). Comparison of chloroethene profiles in the Day 150 core to modeled diffusion profiles indicated degradation occurred in a bioactive zone extending approximately 5 to 6 cm into the clay matrix. These data suggest that a bioactive zone established in a sand-filled fracture can expand into the adjacent clayey till matrix and facilitate mass transfer from the matrix to the bioactive zone. These findings offer promise for ERD and support further development of methods for deploying ERD in clayey till and other low-permeability deposits.

Identification of chlorinated solvents degradation zones in clay till by high resolution chemical, microbial and compound specific isotope analysis

“…These results suggest lower generation of VFA in borehole C compared to A and B. Compared to sites undergoing ERD (Damgaard et al, 2012;Manoli et al, 2011;Scheutz et al, 2010) the concentrations of VFA measured in boreholes A and B are surprisingly high. However, several alcohols (methanol, ethanol, iso-propanol and n-propanol), hydrocarbons and NVOC were found in the groundwater from wells A and B (Table 1).…”

“…The cores were sub-sampled in the laboratory using the procedure described in detail by Scheutz et al (2010). The core was extruded from the stainless steel tube into Rilsan and transferred to a fume hood.…”

“…Analysis of groundwater samples was carried out according to Scheutz et al (2010). The protocol described by Scheutz et al (2010) was used for extraction and analysis of sediment samples (for chlorinated ethenes and ethanes, NVOC, VFA and redox sensitive parameters); however, with minor modifications (described in Appendix A).…”

“…The protocol described by Scheutz et al (2010) was used for extraction and analysis of sediment samples (for chlorinated ethenes and ethanes, NVOC, VFA and redox sensitive parameters); however, with minor modifications (described in Appendix A). Samples for analysis of solid phase Fe(III) were transferred into 10 mL nitrogen flushed glass vials.…”

“…A recent study by Takeuchi et al (2011) documented the presence of Dhc in an organic-rich clayey aquitard undergoing natural reductive dechlorination of PCE to ethene. Findings by Scheutz et al (2010) and Manoli et al (2011) in studies of ERD of chlorinated ethenes in clay tills at two Danish sites (Rugårdsvej and Sortebrovej) suggest, that Dhc are able to spread to the matrix adjacent to induced fractures and natural sand stringers resulting in bioactive zones extending up to 5 cm in the clay till matrix. However, the distribution and expansion of these zones in the matrix have not been investigated/documented.…”