Plume attenuation

Jove-Colon C. F., Brady P. V., Siegel M. D., and Lindgren E. R. (2001) Historical case analysis of uranium plume attenuation. Soil Sedim. Contamin. 10, 71-115. 

Although decay of because of its long half-life of 4.5 billion yr, plays almost no role in U plume attenuation, soil transport of U is affected by most of the processes that control transport of other radionuclides (sorption, indirect effects of biologic activity, etc.) hence consideration of U plumes is a useful starting place. After an overview describing U plume sources, a general review of U chemistry and transport is presented, which is itself followed by a description of plume case studies. The sequence of source identification, fate and transport, and plume description will be the path followed for subsequent treatment of Sr, Cs (half-life = 30.1 yr), Pu, and tritium. 

Ultraviolet laser ablation of polymers spot size, pulse duration, and plume attenuation effects explained./. Appl. Phys., 83, 5458. 

Cooling-Tower Plumes. An important consideration in the acceptabiHty of either a mechanical-draft or a natural-draft tower cooling system is the effect on the environment. The plume emitted by a cooling tower is seen by the surrounding community and can lead to trouble if it is a source of severe ground fog under some atmospheric conditions. The natural-draft tower is much less likely to produce fogging than is the mechanical-draft tower. Nonetheless, it is desirable to devise techniques for predicting plume trajectory and attenuation. 

Ground radiation is from deposited radioactive particles. The deposition rate from a radioactive cloud without rain (dry deposition) is so low that the ground radiation dose is about the same as the inhalation dose. A heavy rain, however, may wash out enough particles from the plume to make ground radiation the dominant contributor to the total dose in a limited area. Rain will also attenuate radiation by leaching the radioactivity to be shielded by the soil and by moving it to streams for further removal. 

Vandenberg JA, Ryan MC, Nuell DD, Chu A (2005) Field evaluation of mixing length and attenuation of nutrients and fecal coliform in a wastewater effluent plume. Environ Monit Assess 107 45-57... 

In the calculation results (Fig. 21.4), benzene again is retarded by sorption and attenuates due to sorption, biodegradation, and dispersion along the direction of flow. In this case, it further attenuates due to transverse dispersion, by mixing with clean water flowing beside the plume. 

Confirmation of certain conditions usually needs to be demonstrated for natural attenuation to be deemed acceptable as a remedial option. This demonstration may involve showing the contaminant plume to be stable and contained, shrinking, or to be intrinsically remediated at the same rate as its spreading (Figure 10.11). When the plume is essentially being remediated at the same rate that it is spreading, dynamic equilibrium conditions exist. 

FIGURE 10.11 Schematic showing natural attenuation scenarios for a contaminant plume when the plume is stable under low-permeability conditions (A), shrinking under high-permeability conditions (B), and reducing via enhanced biodegradation (C). 

No further action may be preferable to natural attenuation in certain instances. Very low risk situations may be better served by no further action since it eliminates the need for continued monitoring and further documentation. Sites with low levels of contaminants or nondiscemible plumes may be better candidates for no further action. Furthermore, very minor releases of hydrocarbons to the subsurface may not be sufficient to support bioremediation. Alternatively, sites with elevated levels of contaminants in nonpotable aquifers may be better addressed through conduct of a risk assessment. 

As a result of the highly reduced state of petroleum hydrocarbons, the preferred and most thermodynamically terminal electron acceptor for microbial processes is oxygen. The inverse relationship between the concentrations of BTEX and dissolved oxygen within a plume is indicative of the extent of microbial metabolism of this class of contaminant. Data from various sites indicate that the natural attenuation of BTEX proceeds at higher rates under oxygenated conditions. The biodegradation of... 

The behaviour of a contaminant plume, whether stable, shrinking or expanding, is predictive for the occurrence of natural attenuation. However, few historical data describing the status of a plume are available. Thus to confirm that natural attenuation processes are taking place, at least four basic conditions must pertain (Azadpour-Keeley et al. 1999), specifically ... 

A water mist system is a proprietary fire protection system using very fine water sprays. The very small water droplets allow the water mist to control or extinguish fires by cooling of the flame and fire plume, oxygen displacement by water vapor, and radiant heat attenuation. These systems are single shot systems. A water mist system and nozzles are shown in Figure 7-28. 

Hydrolysis can explain the attenuation of contaminant plumes in aquifers where the ratio of rate constant to flow rate is sufficiently high. Thus 1,1,1-trichloroethane (TCA) has been observed to disappear from a mixed halocarbon plume over time, while trichlo-roethene and its biodegradation product 1,2-dichloroethene persist. The hydrolytic loss of organophosphate pesticides in sea water, as determined from both laboratory and field studies, suggests that these compounds will not be long-term contaminants despite runoff into streams and, eventually, the sea (Cotham and Bidleman, 1989). The oceans also can provide a major sink for atmospheric species ranging from carbon tetrachloride to methyl bromide. Loss of methyl bromide in the oceans by a combination of hydrolysis... 

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