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Search Result from the November 2002 Issue

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Ramsay, Loren; Jens Brandt Jorgensen, WaterTech A/S. Danish Environmental Protection Agency, Denmark. Environmental Project No 725, p 7-8, 2002 [The above title refers to an English summary. The body of the publication is in Danish. Danish title: Afværge af grundvandsforurening ved kombination af Flushing og MPPE-vandrensning]

Flushing is a remediation technique well-suited for aggressive subsurface treatment of a NAPL-contaminated source area. The method is based on pump-and- treat technology and makes use of chemicals (surfactants, cosolvents, or chemical complexes) added to the aquifer via injection wells. The chemicals change the physical-chemical properties of the NAPL and promote contaminant dissolution and/or mobilization, which enables the removal of the contaminants from extraction wells. Macro Porous Polymer Extraction (MPPE) technology makes use of small hydrophobic particles of plastic placed in a column through which contaminated water is pumped for treatment. A liquid immobilized in the pore structure of the particles removes the contaminants by liquid-liquid extraction. When the column is saturated with contamination, the particles can be regenerated by steam treatment. MPPE has performed well in cases where the concentration of contaminants is high. Flushing typically results in high contaminant concentrations, so combining flushing and MPPE is a logical step. This summary briefly presents two case studies of flushing and MPPE used together to address PCE contamination at former dry-cleaner sites. The first case involved a pilot-scale project--cosolvent flushing with ethanol combined with extracted water treatment by MPPE. The second case involved a 16-day demonstration that applied a flushing mixture of rape seed oil, fatty acids, and glycerol. Approximately 900 cubic meters of ground water were extracted, with an average PCE concentration of 36 mg/L before MPPE treatment and 3 mg/L afterward. Nearly 29 kg of PCE was removed during the demonstration project. Recovery of the surfactant was 82%. Because the PCE concentration in the extracted water did not increase after surfactant injection, the value of the flushing was limited. The MPPE water treatment method was able to remove the PCE from the water/surfactant mixture with good efficiency. MPPE water treatment has functioned as intended in the investigated cases. The disadvantages of combining the technologies include the fact that flushing is a "coarse" method that only removes part of the contamination, so often it is necessary to supplement the method with other approaches for polishing. Flushing also risks spreading the contamination through mobilization. In addition, incomplete recovery will leave some of the chemical additive to remain in the ground water. MPPE is not competitive in situations where the contaminant concentrations are limited. Future prospects for use of flushing/MPPE in Denmark are good because the combined methods are suitable for an initial aggressive remediation of chlorinated solvent NAPL. For more information, visit 2/pdf/87-7972-283-0.pdf

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