Contaminant mobilization

U.S. EPA defines MNA as the reliance on natural processes, within the context of a carefully controlled and monitored site cleanup approach, to achieve site-specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. The natural processes include biodegradation, dispersion, dilution, sorption, volatilization, stabilization, and transformation. These processes reduce site risk by transforming contaminants to less toxic forms, reducing contaminant concentrations, and reducing contaminant mobility and bioavailability. Other terms for natural attenuation in the literature include intrinsic remediation, intrinsic bio-remediation, passive bioremediation natural recovery, and natural assimilation. 30... 

Boyd SA, Lee J-F, Mortland MM (1988) Attenuating organic contaminant mobility by soil modification. Nature 333 345-347... 

By addition of certain chemicals reagents and rigorous mixing, the waste is fixed or stabilized. Contaminant mobility is reduced through the binding of contaminants within a solid matrix, which reduces permeability and the amount of surface area available for the release of toxic components. 

Pozzolanic S/S systems use portland cement and pozzolan materials (e.g., fly ash) to produce a strucmrally stronger waste/concrete composite. The waste is contained in the concrete matrix by microencapsulation (physical entrapment). It is a chemical treatment that uses commercially available soluble silicate solutions and various cementious materials such as cement, lime, poz-zolans, and fly ash. By addition of these reagents and rigorous mixing, the waste is fixed or stabilized. Contaminant mobility is reduced through the binding of contaminants within a solid matrix, which reduces permeability and the amount of surface area available for the release of toxic components. 

Low-permeability soils are difficult to treat with soil flushing. Surfactants can adhere to soil and reduce effective soil porosity. Reactions of flushing fluids with soil can reduce contaminant mobility. 

The surfactants used with the Surtek technology can increase contaminant mobility in two ways. First, they can increase the solubility of the contaminant in water. This process accelerates the removal of sorbed contaminants by increasing their concentration in solution. Second, surfactants can reduce interfacial tension of the NAPLs, which results in direct mobilization. Direct mobilization may allow contaminants to be extracted more efficiently. 

Kaplan, D., Knox, A. Coffey, C. 2002. Reduction of Contaminant Mobility at the TNX Outfall Delta Through the Use of Apatite and Zero-Valent Iron as Soil Amendments. Westinghouse Savannah River Company, Savannah River, Georgia, WSRC-TR-2002-00370. 

Moore, J. N. (1994). Contaminant mobilization resulting from redox pumping in a metal-contaminated river-reservoir system. In Environmental Chemistry of Lakes and Reservoirs, ed. L. A. Baker, pp. 451-71. Washington, D.C. American Chemical Society. Moore, J. N., Ficklin, W. H. Johns, C. (1988). Partitioning of arsenic and metals in reducing sulfidic sediments. Environmental Science and Technology, 22, 432-7. Morrison, G. M., Batley, G. E. Florence, T. M. (1989). Metal speciation and toxicity. Chemistry in Britain, 8, 791-5. 

GROUND-WATER RESTORATION Subsurface Effects of Contaminant Mobility Physical Containment Techniques Hydrodynamic Controls... 

Contaminant Mobilization Resulting from Redox Pumping in a Metal-Contaminated River-Reservoir System... 

Surfactant enhancement is a technology used to remove contaminants from soils and water at hazardous waste sites. The application of surfactants enhances remediation by (a) increasing contaminant mobility and solubility, (b) decreasing the mobility of contaminants, and (c) increasing the rate of biodegradion of contaminants in soil. 

Improperly prepared mobile phase contaminated mobile phase. —> Prepare fresh mobile phase. Check pump-proportioning valve for malfunction. 

Contaminant mobilization resulting from redox pumping in a metal-contaminated river-reservoir system. Environmental Chemistry of Lakes and Reservoirs Advances in Chemistry Series, p. 451-471. 

Comparing the modeling results with site monitoring data shows that the predicted sequence of the contaminant mobility, Be < Cd < Ni < U, is consistent with the metal distribution at the site. Surface complexation has essentially immobilized Be and Cd... 

On-site treatment may be proposed if it is determined that the release of contaminants presents an unacceptable risk. Leaching tests can be carried out on the treated soil to monitor whether the treatment has achieved the intended reduction in contaminant mobility. 

McCarthy JF, Zachara JM (1989) Subsurface transport of contaminants Mobile colloids in the subsurface environment may alter the transport of contaminants. Environ Sci Technol 23, 496-502. 

Modeling Contaminant Mobilization and Transport through Sediments... 

Human health risk assessment involves identifying and characterising contamination hazards on sites defining contaminant mobility developing realistic scenarios in which humans could be exposed to contaminants estimating the uptake of a contaminant by humans and finally evaluating the consequences of the uptake. 

In this study 154 exposed and 155 unexposed persons were examined. The exposed persons had been living in a mobile home park in which 2,3,7,8-TCDD contaminated waste oil was sprayed for dust control. The TCDD contamination dated back to 1971 when TCDD-contaminated sludge wastes were taken from a hexachlorophene production facility (11,52) Levels of 2,3,7,8-TCDD up to 2.2 ppm (mg/kg) were still present more than ten years later. No increased clinical illness was noted in the group who had lived in the contaminated mobile... 

During this very long time period, processes may occur under the impact of changing hydrochemical conditions that lead to a new phase of contaminant mobilization. It is easy to visualize how a process may be initiated when oxidized precipitation infiltrates a post-methanogenic landfill body and a front of increased metal concentrations moves toward the groundwater over a long period of time as a consequence of dissolution and precipitation reactions (Fbrstner et al. 1987). This possibility of metal mobilization from reactor landfills should always be considered when low-organic hazardous waste is deposited, especially if it contain sulfides or easily soluble components. 

The case study illustrates the importance of applying a range of techniques for the investigation of contaminant metal speciation. In the absence of SEM-EDS data, it would not have been possible to determine that the Pb in the off-site soil was precipitated on clay floes. Hence the distinction between primary contamination (i.e. lead particulates), and secondary contamination mobilized from the original contamination could not have been made. Conversely, SEM-EDS failed to detect zinc, and without sequential extraction data and surface water analysis the mobility of this metal would not have been apparent. 

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