Thousands of Department of Defense (DoD) sites and installations are contaminated with organic pollutants and require remediation. Performing this remediation in situ is an attractive and cost-effective alternative that eliminates the need for excavation and transportation of large volumes of contaminated material. However, a key limitation to effective in situ bioremediation is timely introduction of reactive agents and biological amendments. Development of a technology for uniform introduction and mixing of additives remains a bottleneck to the successful field application of in situ remediation technologies.
The objective of this project was to use subsurface electrodes to induce a potential across contaminated soil systems, thereby mobilizing amendments through the contaminated zone and resulting in accelerated in situ remediation conditions. The efficiency of additive transport and mixture in low permeability and heterogeneous soils was evaluated.
The ability to use induced electrical fields to transport additives in soils was demonstrated in the laboratory using model soil systems. Additive transport was measured in systems with limiting conditions including soil type, hydraulic conductivity, and pH. Two soils of varying permeability used throughout this study included a fine sand and a sandy clay. Experiments evaluated transport under homogenous and heterogeneous (stratified) conditions using three additives: two organics (lactate and citrate) and one inorganic (permanganate). The effectiveness of this unique delivery system was tested using both cross-injection and mixing under single-phase and dual polarity pulse direct current fields and associated electrochemical redox reactions.
This project demonstrated the potential of injecting negatively charged amendments to stimulate bioremediation. Citrate and lactate delivery under 1V/cm in wells spaced 40cm apart translated into an equivalent hydraulic head for the citrate and lactate delivery of 60 and 85 meters, respectively. Further, electrokinetically delivered amendments appeared to negate amendment delivery short-circuiting in high permeability areas, and biological activity increased without problematic biofouling.
The transport of amendments in low permeability soils has been a limiting factor in the successful application of many in situ technologies. Electrokinetic-assisted amendment transport has the potential to reduce cleanup costs and enable in situ technologies to be more effectively applied in low permeability soils.