US Department of Defense (DoD) has estimated significant cost savings are possible through the application of accelerated source treatment technologies at DoD sites where long-term hydraulic containment is the implemented remedy.
In-situ bioremediation has been considered as one of the most cost-effective remedial options; however, the success of in-situ remediation depends heavily on effective delivery of remediation reagents. In 2011, a workshop commissioned by DoD's research and development programs, SERDP/ESTCP, identified that innovative, cost-effective techniques for delivering remedial reagents to low-permeability (low-K) zones as a high priority area requiring technology development initiatives.
Electrokinetic (EK) enhanced amendment delivery is an innovative technology that uses low-voltage direct current (DC) to uniformly transport amendments through clays and silts. EK transport mechanisms (electromigration and electro-osmosis) are related to soil's electrical properties, and, therefore, not substantially affected by soil hydraulic conductivity. Geosyntec, in collaboration with NAVFAC and the US Army Corps of Engineers, was funded by ESTCP to demonstrate EK-BIOTM in achieving enhanced reductive dechlorination of PCE residing in a clay unit underlying a sandy aquifer at Naval Air Station Jacksonville (NAS JAX) in Florida.
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Previous investigations of the target area revealed a classic contaminant distribution profile showing that PCE had migrated vertically through the shallow sandy aquifer and into the underlying clay materials. Geosyntec first conducted a bench-scale evaluation using site aquifer materials to determine the EK transport rate of mono-valent anion. The team subsequently designed and installed a network of 9 electrode wells within the target treatment area (approximately 35 ft by 35 ft), as well as an EK control system consisting of a DC power supply unit, a manifold system to supply amendments (lactate and carbonate buffer solutions), and a system that monitors and controls the pH in electrode wells. The target area was also bioaugmented with dechlorination microbial culture, KB-1®, during technology demonstration. The system operation was conducted in 2 separate stages, with each stage lasted approximately 5 months and each with a different electric field orientation created by powering the electrode network using approximately 9A at 15V to 25V.
This project is the first rigorous field-scale demonstration of EK-BIOTM in the US. The performance monitoring data showed that the project had met the demonstration objectives with >80% of PCE decrease coupled with substantial increases of dissolved ethene, as well as >100x increases of biomarkers (Dehalococcoides, Dehalobacter, and vinyl chloride reductase (vcrA) genes) specifically in the clay materials within the treatment area. The low electrical energy applied during this demonstration (e.g., below 10A and 30V) reflected the excellent sustainability performance of this technology. Geosyntec has demonstrated through this project that EK-BIOTM represents an innovative, cost-effective solution for the vexing problem of remediating chlorinated solvents in low-K materials and in aquifers with highly heterogeneous permeability.