Site remediation approach. At the Sortebrovej site an emulsified oil donor (EOS) and a bio-augmentation culture (KB1®) with specific degraders Dehalococcoides were injected in a net-work of screened wells and spread in natural sand stringers embedded in the clay till. At the Gl. Kongevej site organic molasses donor and Bioclear Dechlorinating bioaugmentation culture with specific degraders Dehalococcoides were injected with a drive-point probe (Geoprobe) at 25 cm spaced vertical intervals in the clay till in a closely spaced network.
Investigative activities. An integrated investigative approach consisting of water and clay core sample analysis, including stable isotopes and specific degraders, as well as analysis for chlorin-ated solvents, degradation products, donor fermentation products and redox sensitive parameters combined with modelling was applied. Groundwater monitoring of selected wells was performed 2-3 times per year, and very detailed subsampling (on 0.25-5 cm scale) of the intact clay cores for matrix profile analysis was performed after 2 and 4 years. The transport including matrix diffu-sion and degradation in fractures/sand stringers and in bioactive zones in the clay till adjacent to the fractures/sand stringers was modelled to gain insight on the effects of sand stringer/fracture /injection spacing, thickness of bioactive zones, density/numbers of specific degraders, donor longevity, etc., on remediation efficiency and timeframes.
Results/Lessons learned. The results showed that the chlorinated solvent TCE was converted into its daughter products (DCE, VC and ethene) but complete conversion of contaminants to ethene (as expected) was not achieved in 4 years. Large variation in the effect of ERD in the clay matrix between sites, boreholes and even between cores was observed. After 4 years, the mass removal at the 2 sites varied between <5% and 50% within the treated zones. The limited effi-ciency of the bioremediation in terms of mass removal is due to the limited spatial extent of dechlorination. If degradation is restricted to narrow bioactive zones of a few cm developing around fractures and sand stringers, contaminants in the remaining part of the matrix are not de-graded and remediation efficiency is low due to the mass transfer limitations. However, the bio-active zones may expand in zones where both donor and chlorinated compounds are present. And in some cores TCE was depleted (degraded to DCE) in zones up to 1.8 m thick, an extent, which could not be explained by diffusive loss to narrow bioactive zones. Hence, biomass migration in the clay matrix appears to play an important role in terms of contaminants mass reduction.
|Number of pages||1|
|Publication status||Published - 2012|
|Event||International Conference on Advanced Environmental Science and Technology (AEST12) - Seoul, Korea, Republic of|
Duration: 26 Aug 2012 → 30 Aug 2012
|Conference||International Conference on Advanced Environmental Science and Technology (AEST12)|
|Country||Korea, Republic of|
|Period||26/08/2012 → 30/08/2012|