Field Test of Cyclodextrin for Enhanced In-Situ Flushing of Multiple-Component Immiscible Organic Liquid Contamination: Project Overview and Initial Results

Abstract

The purpose of this paper is to present an overview and the initial results of a pilot-scale experiment designed to test the use of cyclodextrin for enhanced in-situ flushing of an aquifer contaminated by immiscible liquid. This is the first field test of this technology, termed a complexing sugar flush (CSF). The field test was conducted within a solvent and fuel disposal site at Hill Air Force Base, UT. The cyclodextrin solution increased the aqueous concentrations of all the target contaminants to values from about 100 to more than 20000 times the concentrations obtained during the water flush conducted prior to the CSF. Concomitantly, the CSF greatly enhanced the rate of mass removal during the 8 pore-volume flush, which resulted in a 41 % reduction in contaminant mass. Based on these results, it is clear that the CSF technology was successful in enhancing the remediation of the immiscible-liquid contaminated site. There are several attributes of cyclodextrin that in some situations may offer advantages compared to using surfactants or cosolvents for solubilization-based enhanced flushing.The limitations of current technologies for cleaning up sites contaminated by immiscible liquids are well known (e.g., 1). This has lead to a search for alternative technologies. One approach that is receiving serious consideration involves the use of a flushing solution containing a chemical agent that can greatly increase the mass of contaminant held in the aqueous phase. These enhanced solubilization agents include surfactants, cosolvents, and complexing agents (e.g., dissolved organic matter, 118In Innovative Subsurface Remediation; Brusseau, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1999. 119 cyclodextrin). Surfactants, and cosolvents to a lesser extent, have received the majority of attention to date. While these agents have several advantageous properties, and have been used successfully for enhanced flushing, they also have some disadvantages. Thus, investigation of alternative agents continues.The purpose of this paper is to present an overview and the initial results of a pilot-scale experiment designed to test the use of cyclodextrin for enhanced in-situ flushing of an aquifer contaminated by immiscible organic liquid. The field test was conducted within a site at Hill Air Force Base, Utah, that is contaminated with a complex, multiple-component, immiscible organic liquid comprised of fuels and spent solvents. The study was conducted as part of a project organized by the Environmental Protection Agency National Research Laboratory, Ada, OK, which was funded by the SERDP Program of the U.S. Department of Defense. The purpose of the project was to evaluate the performance of several innovative remediation technologies, implemented simultaneously at the same site (2). BACKGROUND Basic Properties of CyclodextrinThe compound used in the experiment was hydroxypropyl-P-cyclodextrin (HPCD), which consists primarily of glucose molecules. Cyclodextrins are cyclic oligosaccharides produced ...

Remediation of NAPL Source Zones: Lessons Learned from Field Studies at Hill and Dover AFB

“…The University of Arizona (McCray and Brusseau 1998, 1999; Brusseau et al 1999a; McCray et al 1999) conducted the field test of cyclodextrin‐flushing for cleanup of a contaminated site at Hill AFB. The technology was termed a “Complexing‐Sugar Flush” (CSF).…”

“…The aquifer has a horizontal hydraulic conductivity of about 0.05 cm/s and an effective porosity of 20%. The average vertical hydraulic conductivity of the clay unit is less than 10 −7 cm/s based on constant‐head testing of core samples collected from the unit (Brusseau et al 1999a). Several waste sites areas are located within OU1 that were in operation at various times between 1940 and 1978.…”

“…These compounds comprise slightly less than 10% of the total NAPL within the cell. The remainder was comprised primarily of higher molecular‐weight jet fuel components and relatively insoluble, pitch‐like components, some of which could not even be extracted using a solvent (Rao et al 1997; Brusseau et al 1999a).…”

“…Natural groundwater levels in the test cells generally ranged between 8 to 10 m bgs (Dover) and 3 to 4 m bgs (Hill) prior to each experiment. For details of test cells and instrumentation at the Hill and Dover sites, the reader is referred to (Brusseau et al 1999a; Wood and Enfield 1999, 2005; Brooks et al 2002; Tick et al 2003; Childs et al 2004, 2006). The remediation “treatment zone” for each technology at both Hill and Dover is assumed to include the entire saturated thickness within each test cell, and treatment‐zone volumes are reported in Table 1.…”

“…This led to debate and ongoing research on partial source‐zone removal. Data from these and subsequent studies show that reduction in groundwater concentrations and mass flux are highly correlated to source‐zone NAPL removal and that alternative methods such as mass flux reduction may be more appropriate for evaluating risk assessment rather than relying on point concentration reductions. The effectiveness of characterization methods (PTTs, soil cores, groundwater sampling) are somewhat site specific (e.g., Brusseau et al 1999a; Jawitz et al 2003b), and possibly even technology specific (e.g., Dugan et al 2003), and thus are not highly reliable for assessing remediation effectiveness by themselves. However, using multiple methods, each of which may give a different removal assessment, enables the user to better quantify the uncertainty associated with the mass estimates.…”