Formatted Title
Remedial Approach for In Situ Treatment of Deep CHC Contaminants Underlying a Manufacturing Site in Germany Using ZVI and Bioaugmentation
Background/Objectives
Background/Objectives
Due to its heavy industrialization and densely populated urban areas, in situ remedial approaches are often the most practical and cost-effective means of mitigating contamination at industrial sites in Germany. Site owners are frequently faced with untenable cost burdens or disruptions to commercial operations when considering traditional remediation technologies. The Dexion GmbH operation in Laubach, Germany, manufactures industrial shelving and modular storage systems, whereby past activities associated with metal degreasing and enamel/paint coating activities have resulted in subsurface chlorinated hydrocarbon (CHC) impacts up to 22 m below ground surface, which largely underlie the existing plant facilities. Soil excavation and ex situ remedial options were initially considered, but deemed impractical due to i) the necessity of demolishing much of the plant infrastructure to gain access to contaminated sediments, ii) lost manufacturing capacity, and iii) exorbitant costs. Pump and treat measures only provide limited effectiveness due to the low permeability of underlying silty clay soils. An in situ remedial alternative approach was therefore investigated to effectively mitigate CHC contaminants using highly targeted emplacement of treatment reagents. Objectives of the work were to:
- Conduct a pilot-scale application to determine the most favorable treatment approach for the given site conditions and contaminant concentrations, and
- Implement the selected remedial process/technologies as full-scale site remediation.
Approach/Activities
Approach/Activities
A field pilot trial was conducted in two separate contaminant plume areas at the site to evaluate and compare the performance of in situ chemical oxidation (ISCO) to in situ bioremediation (ISB) with biological augmentation. The results after 2 years of monitoring indicated that both approaches had reduced ∑CHC concentrations by approximately 50%, although rebound effects were apparent in the ISCO trial (after depletion of the persulfate oxidant) which was not the case for the ISB trial. Therefore, a remedial approach for full-scale in situ treatment of the site was developed using in situ chemical reduction (ISCR) with ISB. Targeted solids emplacement (“TSE”) technology using direct push drilling and custom manufactured mixing and pumping equipment was applied for full-scale treatment using Evonik’s EHC® amendment (a mixture of organic carbon and micro-ZVI). A total of 40 metric tons of amendment was injected into low permeability soils located under the plant infrastructure. After injection, each of the 40 injection points were constructed as injection wells for the infiltration of lab cultivated microorganism cultures containing the species Dehalococcoides mccartyi (DHC-M) to further stimulate anaerobic dechlorination. This was followed by a comprehensive groundwater sampling program.
Results/Lessons Learned
Results/Lessons Learned
Groundwater monitoring results from a network of 13 monitoring wells and 40 injection wells within and proximate to the contaminant plume have demonstrated a median reduction to date of 66% total CHCs (including chloro-methanes/ethanes), despite the low permeability of clay soils. Effectiveness of ongoing contaminant degradation since the beginning of pilot-scale work is largely attributable to i) the unique mode of amendment emplacement (soil fracturing), which provides a greater ROI and shortening of diffusion pathways for treatment, and ii) the longevity of EHC. The effectiveness of DHC-M bio-enhancement, which has not yet reached its full potential based on the results of qPCR analysis, is thereby also improved. Ongoing groundwater monitoring in the context of remedial process optimization has identified a few isolated areas of contaminant rebound where additional treatment may be necessary.