Subsurface Processes

Release of organic chemicals can occur under a wide variety of scenarios and environmental settings. The extent of any threat to human health and the environment depends on release-specific conditions. Some of the factors that determine the risk include  

Once released, the organic chemical interacts physically with soil and water by one or more distinct processes  

FIGURE 5.3 Stages of subsurface hydrocarbon migration. (After Schwille, 1967.) 

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Layadi et al. have shown, using in. situ spectroscopic ellipsometry, that both surface and subsurface processes are involved in the formation of /xc-Si [502, 503]. In addition, it was shown that the crystallites nucleate in the highly porous layer below the film surface [502, 504], as a result of energy released by chemical reactions [505, 506] (chemical annealing). In this process four phases can be distinguished incubation, nucleation, growth, and steady state [507]. In the incubation phase, the void fraction increases gradually while the amorphous fraction decreases. Crystallites start to appear when the void fraction reaches a maximum... 

This method assumes that if two or more contaminants were released from a single, slug-type release, the date upon which these contaminants entered the water table or aquifer is equivalent to the time when their relative concentrations were the same as the source material. This method does not require initial concentration information, and is not dependent on changes due to a particular subsurface process (i.e.,... 

The ability to measure the isotopic composition of individual compounds can be used to determinate whether or not some contaminants are being affected by surface/subsurface processes. In comparison, monitoring the isotopic composition of total carbon can only provide information concerning the processes affecting the contaminant mixture as a whole rather than individual compounds. 

Rouxel O, Fouquet Y, Ludden JN (2004) Subsurface processes at the Lucky Strike Hydrothermal Field, Mid-Atlantic Ridge Evidence from sulfur, selenium, and iron isotopes. Geochim Cosmochim Acta, submitted... 

Rouxel O, Eouquet Y, Ludden JN (2004) Subsurface processes at the Lucky Strike hydrothermal field, Mid-Atlantic Ridge evidence from sulfur, selenium and iron isotopes. Geochim Cosmochim Acta, in press Schauble EA, Rossman GR, Taylor HP (2001) Theoretical estimates of equilibrium Ee-isotope fractionations from vibrational spectroscopy. Geochim Cosmochim Acta 65 2487-2497 Schopf JW (1992) Paleobiology of the Archaen. Im The Proterozoic Biosphere A Multidisciplinary Study. Schopf JW, Klein C (eds) p 25-39... 

Some of the basic processes in the formation of secondary porosity are similar to those for formation of carbonate cements. A solution of proper composition must be generated by subsurface processes, and this solution must also flow through the formation in which the dissolution reaction takes place in sufficient quantities to transport the dissolved carbonate. The primary differences between cement and secondary porosity formation are that an undersaturated solution must be generated rather than a supersaturated solution, and that while cement formation reduces porosity and can inhibit flow, formation of secondary porosity increases porosity and can result in enhanced flow of subsurface fluids. 

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