A significant portion of the near-surface geology in Denmark consists of glacial moraine deposits, much of which consists of clayey till. Consequently, subsurface releases and spills of chlorinated solvents at industrial facilities in Denmark often end up as a sorbed phase or dense nonaqueous phase liquid (DNAPL) that resides in clayey till.
In situ remediation technologies that may succeed in sand and gravel aquifers often fail at sites with clayey till. Electrokinetic-enhanced bioremediation (EK-BIO) is an innovative technology for addressing low-permeability formations through the application of direct current (DC) electric fields to facilitate subsurface transport and delivery of bioremediation agents such as electron donors and dechlorinating bacteria. Recognizing that Geosyntec is one of the only engineering consulting firms that possesses expertise with this technology, the Capital Region of Denmark retained the team of Geosyntec, NiRAS, and the U.S. Army Environmental Research and Development Center (ERDC) to design and execute an EK-BIO pilot test at a clayey till site in Denmark.
Geosyntec's Scope of Services for Electrokinetic-Enhanced Bioremediation of Chlorinated Solvents in Denmark
Geosyntec first directed a bench-scale treatability test in collaboration with ERDC and Northeastern University. PCE-impacted clayey soil from the test site was consolidated into EK reactors. A DC power supply maintained a current density of 0.5 A/m2 across the reactor. With lactate as electron donor, and augmented with a dechlorinating microbial culture (KB-1®) that contains Dehalococcoides bacteria (Dhc), complete PCE dechlorination across the clayey soil reactor was demonstrated. Geosyntec subsequently led the design of an EK-BIO field pilot test, performed start-up operation, and directed system O&M and data analysis. An array of 3 cathodes and 3 anodes were installed across a test area of approximately 3 m x 2 m with a target treatment depth interval from 3 m to 8 m. Following 74 days of EK operation (55 days after bioaugmentation) to transport lactate and augmented bacteria, enhanced reductive dechlorination was demonstrated in the clay materials within the test area.
Notable Accomplishments for Electrokinetic-Enhanced Bioremediation of Chlorinated Solvents in Denmark
This project is the first rigorous field pilot test of EK-BIO, including a bioaugmentation element, in the world. The lactate transport rate in the test area was estimated to range from 2.5 to 5 cm/day. Microbial data (molecular testing for Dhc and the vinyl chloride reductase gene) indicated that the EK process was successful in distributing Dhc within the clay materials in the test area. Active reductive dechlorination was promoted, as indicated by evident increases of degradation products (cis-DCE, VC and ethene) and Dhc levels. The ongoing success of this project suggests that EK-BIO may offer a cost-effective solution for the vexing problem of chlorinated solvents in low-permeability materials and sites with high degrees of heterogeneity in formation permeability.