U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

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U.S. EPA Technology Innovation and Field Services Division

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Baldock, J., P. Crowcroft, A. Peacock, Z. Gillingham, A. Sykes, A. Thomas, J. Teer, M. Klabun, and R. Timson. Seventh International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2010). Battelle Press, Columbus, OH. ISBN: 978-0-9819730-2-9, Paper E-042, 4 pp, 2010

Potential trichlorobenzene (TCB) DNAPL source zones were identified at a 1.9-ha dye works site within the underlying heterogeneous clay, silt, sand, and gravel aquifer. The aquifer is in hydraulic continuity with an adjacent river. Following the completion of lab tests confirming potential applicability, a full-scale surfactant-enhanced recovery system was installed to address DNAPL and dissolved-phase constituents in groundwater. Operation was implemented within a relatively short period, between July 2008 and February 2009. The system is believed to be the first full-scale surfactant-enhanced recovery project undertaken within an aquifer in the United Kingdom. Twenty-three injection/extraction wells installed across an area of ~800 sq m delivered a mixture of two commercially available surfactants either under pressure or via gravity drainage, depending on subsurface permeability. The source zone was subdivided into 5 cells of 4 to 5 wells each and targeted with four flushes of surfactant, each with a defined contact time. Whilst one cell was under injection, another would be extracted, with the remainder in contact. Contact time, optimized in lab tests, was critical to success. Extraction for aboveground treatment took place after 7 days of equilibration and mobilization of the chlorinated benzenes. To minimize the risk of contaminant migration away from the treatment zone, injection and extraction were conducted simultaneously to maintain a neutral water balance within the aquifer. This process was repeated for 3 months, with surfactant recycling, until TCB concentrations reached baseline within each well. The operation involved injection of 1,000 m3 of surfactant solution, extraction of >7,000 m3 of groundwater, and treatment in a system comprising groundwater influent tanks, sediment filters, a photocatalytic UV reactor, and liquid-phase carbon filters. This effort recovered ~2,650 kg of contaminants. The project also developed an analytical method that enabled concentrations of TCB and DCB to be determined in the presence of surfactants, a process not available in external commercial laboratories in the UK. As a polishing step, a total of 3,030 m3 of emulsified vegetable oil was injected to encourage further reduction of residual contamination via anaerobic degradation. Additionally, a zero-valent iron permeable reactive barrier was installed at the base of the river.

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