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ENVIRONMENTAL RESEARCH BRIEF: SURFACTANT-ENHANCED DNAPL REMEDIATION: SURFACTANT SELECTION, HYDRAULIC EFFICIENCY, AND ECONOMIC FACTORS
Citation:
Sabatini, D. A., R. C. Knox, AND J. H. Harwell. ENVIRONMENTAL RESEARCH BRIEF: SURFACTANT-ENHANCED DNAPL REMEDIATION: SURFACTANT SELECTION, HYDRAULIC EFFICIENCY, AND ECONOMIC FACTORS. EPA/600/S-96/002, 1996.
Impact/Purpose:
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Description:
Chlorinated hydrocarbons are ubiquitous ground water contaminants due to their widespread use as organic solvents and cleaners/degreasers. The immiscibility of chlorinated organis with ground water causes them to exists as nonaqueous phase liquids (NAPLs); this results in their occurrence in the subsurface as residual and free phases. Having a density greater than water, they are often referred to as dense nonaqueous phase liquids (DNAPLs). Water solubilities of these chlorinated hydrocarbons are frequently several orders of magnitude above their drinking water standards, yet low enough to limit dissolution during pump-and-treat remediation. remediation of residual DNAPL contamination can require hundreds to thousands of flushings of the ground water (pore volumes) using conventional pump-and-treat methods. Strongly sorbing (hydrophobic) compounds will experience a similar fate (e.g., PAHs, PCBs) The inefficiency of conventional pump-and-treat methods for these contaminants has recently been addressed, with surfactants being mentioned as a promising technology for enhancing conventional approaches. Two obstacles to widespread implementation of surfactant-enhanced subsurface remediation are (1) gaining regulatory approval for the injection of surfactants, and (2) the economics as impacted by surfactant costs (suggesting minimization of hydraulic and physicochemical surfactant losses). The objective of this brief is to present research results addressing these two issues, as further delineated below. Of course, proper surfactant selection is imperative to successful enhancement of DNAPL extraction; factors affecting surfactant selection are discussed in this document. Gaining regulatory approval is an obstacle common to all chemical amendmenetes being considered for subsurface remediation. Surfactants with U.S. Food and Drug Administration direct food additive status and which are commonly used in consumer products are the focus of this research. The economics of surfactant-enhanced remediation processes will potentially be limited by surfactant losses in the subsurface, including hydraulic losses to uncontaminated portions of the aquifer and physicochemical losses (e.g., sorption, precipitation). Hydraulic approaches for discussion of vertical circulation wells. Finally, results of a preliminary economic analysis for surfactant-enhanced DNAPL remediation are presented, along with suggestions for optimizing the economics of this technology.