Migrating contaminants

Electric fields use in soil restoration has been focused on contaminant extraction by their transport under electroosmosis and ionic migration. Contaminant extraction by electric fields is a successful technique for removal of ionic or mobile contaminants in the subsurface. However, this technique might not be effective in treatment of soils contaminated with immobile and/or trapped organics, such as dense non aqueous phase liquids (DNAPLs). For such organics, it is possible to use electric fields to stimulate in situ biodegradation under either aerobic or anaerobic conditions. It is necessary to evaluate the impact of dc electric fields on the biogeochemical interactions prior to application of the technique. It is not clear yet how dc electric fields will impact microbial adhesion and transport in the subsurface. Further, the effect of dc fields on the activity of microorganisms in a soil matrix is not yet well understood. 

Kleinschnitz M, Schreier P (1998) Identification and Semi-quantitative Determination of a Migration Contaminant from Beverage Carton Packages into Mineral Water by On-line Solid Phase Extraction Gas Chromatography-Mass Spectrometry (SPE-GC-MS). Chromatographia 48, 581-583. 

Foodstuffs, pharmaceuticals, toiletries, cosmetics, etc. must avoid contaminants derived by direct contact or by migration from printing inks. Food grade inks can be specified. See also migration/contamination/reaction below. 

Monitored Natural Attenuation involves the monitoring of the subsurface environment and processes to evaluate whether natural attenuation processes are sufficient to ensure an adequate reduction of contaminant concentration by the time the migrating contaminated groundwater reaches a receptor (see Section 3, Monitored Natural Attenuation, below). 

The reactive barriers can be installed across the path of a migrating contaminant plume to prevent further plume growth, or constructed immediately downstream of a contaminant source to prevent plume development. As the contaminant plume passes through the barrier the contaminants are either removed by the barrier and immobilised or are transformed into less harmful compounds. A range of treatment processes can be used within reactive barriers to treat both organic and inorganic contaminants.29,31 These include ... 

Groundwater. One approach to minimizing the environmental impact of excess nitrogen in groundwater migrating into rivers and aquifers is to intercept the water with rapidly growing trees, such as poplars, that will use the contaminant as a fertilizer. 

Eor high value food packaging appHcations, minimal migration of contaminants into food products is critical. Currently the PDA requirement is a maximum 0.5 parts per biUion (ppb) of noncarcinogenic compounds by dietary exposure (22). 

Mechanical Gleaning. A cleaner is a hydrocyclone device utilizing fluid pressure to create rotational fluid motion (20). Pulp is introduced tangentially near the top of the cleaner. Contaminants denser than water such as chemically treated toner inks and sand migrate toward the outer wall of the cleaner and exit in a separate (reject) stream. For most forward cleaners, optimal ink removal efficiency is obtained at a pulp consistency of 0.2—0.3%. Most forward cleaners deinking efficiency declines at pulp feed consistencies greater than 0.4%. However, a cleaner said to be efficient at 1.2% pulp consistency has been reported (39). 

Reverse cleaners operate on the same principles as forward cleaners (20). Contaminants less dense than water migrate toward the center of the cleaner and exit as a separate (reject) stream from the pulp slurry. Reverse cleaners are used to remove adhesive and plastic particles as well as paper filler particles and lightweight particles formed from paper coatings. 

Hydrocarbon sensors (qv) placed directiy below the tank bottoms can be effective. However, old contamination or contamination from other tanks or piping can yield misleading results. In addition, the low permeabUity of some areas in the soil can prevent the migration of vapors to the sensing ports under the tank bottom. 

Nonaqueous phase Hquids (NAPLs) present special problems for soil and ground water cleanup. Contaminant transport through ground water depends in part on the water solubiHty of the compound. Because NAPLs cling to subsurface particles and are slow to dissolve in ground water, they hinder cleanups and prolong cleanup times. Dense nonaqueous phase Hquids (DNAPLs) migrate downward in the aquifer and can coUect in pools or pockets of the substmcture. Examples of DNAPLs are the common solvents tetrachloroethylene (PCE) and trichloroethylene (TCE) which were used extensively at many faciHties before the extent of subsurface contamination problems was realized. 

Plume Containment. WeUs can be placed at a contaminated site to prevent the contamination from spreading further or migrating offsite. In the past, containment efforts often reHed on physical methods such as bentonite slurry trenches, grout curtains, sheet pilings, weU points, and fixative injections. Containment by judiciously placed weUs generally costs less, takes less time to install, and is more flexible because pumping rates and locations can be varied. 

Use of DMF as a solvent for the oxidation of l-o1efins has been reported by Clement and Selwitz. The method requires only a catalytic amount of PdCl2 and gives satisfactory yields under mild conditions. A small amount of olefin migration product is the only noticeable contaminant in the cases reported. The procedure can be applied satisfactorily to various 1-olefins with other functional groups. This useful synthetic method for the preparation of methyl ketones has been applied extensively in the syntheses of natural products such as steroids,macrolides, dihydrojasmone, and muscone. " A comprehensive review article on the palladium-catalyzed oxidation of olefins has... 

Contaminant transfer to bed sediments represents another significant transfer mechanism, especially in cases where contaminants are in the form of suspended solids or are dissolved hydrophobic substances that can become adsorbed by organic matter in bed sediments. For the purposes of this chapter, sediments and water are considered part of a single system because of their complex interassociation. Surface water-bed sediment transfer is reversible bed sediments often act as temporary repositories for contaminants and gradually rerelease contaminants to surface waters. Sorbed or settled contaminants are frequently transported with bed sediment migration or flow. Transfer of sorbed contaminants to bottomdwelling, edible biota represents a fate pathway potentially resulting in human exposure. Where this transfer mechanism appears likely, the biotic fate of contaminants should be assessed. 

The most significant contaminant movement in soils is a function of liquid movement. Dry, soluble contaminants dissolved in precipitation, run-on, or human applied water will migrate through percolation into the soil. Migration rates are a function of net water recharge rates and contaminant solubility. 

Weak boundary layer. WBL theory proposes that a cohesively weak region is present at the adhesive-substrate interface, which leads to poor adhesion. This layer can prevent the formation of adhesive bonds, or the adhesive can preferentially form bonds with the boundary layer rather that the surface it was intended for. Typically, the locus of failure is interfacial or in close proximity to the silicone-substrate interface. One of the most common causes of a WBL being formed is the presence of contaminants on the surface of the substrate. The formation of a WBL can also result from migration of additives from the bulk of the substrate, to the silicone-substrate interface. Alternatively, molecular... 

Early in the Corrective Action process, a decision may be made concerning whether or not containment is necessary to protect human health and the environment (HHE). If the release or threatened release presents danger to HHE, immediate action must be taken to halt migration. Under these circumstances, actions termed "Interim Measures" may be required, and excavation or containment measures may be directed by the regulatory agency. However, the Owner/Operator will be responsible for their implementation. In the event that containment is not required as an interim measure, containment may still be needed as part of the overall Corrective Action to halt the pollution migration if wastes or contaminants are to be left on-site. 

Identify most likely pathways of contaminant migration... 

Determine maximum potential migration rate and dispersion of contaminants... 

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