Near-surface conditions

Table 20.4 presents the partition and transformation processes known to occur in the near-surface environment along with the special factors that should be considered when evaluating data in the context of the deep-well environment. Geochemical processes affecting hazardous wastes in deep-well environments have been studied much less than those occurring in near-surface environments (such as soils and shallow aquifers). Consequently, laboratory data and field studies for a particular substance may be available for near-surface conditions, but not for deep-well conditions. 

Biodegradation Partly Some near-surface bacteria appear capable of entering and surviving in the deep-well environment. However, in general, temperature and pressure conditions in the deep-well environment are unfavorable for microbiota that are adapted to near-surface conditions. Biological transformations are primarily anaerobic. 

Greater pressures tend to decrease the growth and survival of bacteria, but for certain species increased temperature counters this effect. For example, the growth and reproduction of E. coli essentially stops in nutrient cultures at 20°C and 400 atm (40.5 MPa). When the temperature is increased to 40°C, however, growth and reproduction are about the same as at near-surface conditions.74... 

The Langmuir model has been used to describe adsorption behavior of some organic compounds at near-surface conditions.137 However, three important assumptions must be made ... 

It would appear from the above summary of natural occurrences that quartz is the most stable form of silica at near-surface conditions but that other metastable phases, representing initially poorly organized material, predominate in the natural occurrences or newly formed silica. Experiments demonstrate the persistence of metastable amorphous or cryptocrystalline hydrated Si02 at low temperature (Kittrick, 1969 Krauskopf, 1956, 1959) and slow conversion at higher temperatures (above 100 bars) (Frondel, 1962 Heydemann, 1964 Carr and Fyfe, 1958 Mlzutanl, 1970). 

Wogelius R. A. and Walther 1. V. (1992) Olivine dissolution kinetics at near-surface conditions. Chem. Geol. 97(1-2), 101-112. 

If pyrite is the source of arsenic in the Marshall Sandstone aquifer, its oxidation must have occurred at surface or near-surface conditions. Weathering of detrital Marshall Sandstone and Michigan Formation shale in tills could explain the presence of arsenic-rich wells in glacial aquifers. However, high levels of arsenic are more common in the bedrock aquifer than in glacial aquifers, and in both aquifers, the distribution of such wells is scattered. Bedrock samples show the distribution of authigenic pyrite to be very patchy, and not all of the pyrite is arsenic-rich. Therefore, even in the case of pyrite oxidation at depth in a bedrock aquifer, we would expect local... 

All solubility calculations to date assume ideal gas behavior for the noble gases irrespective of geological environment. At near surface conditions, Lewis-Randall mixing is a reasonable assumption. It is clear from Figure 2, that the assumption of ideal behavior for He, Ne, and Ar at near surface conditions is also reasonable. More care must be taken with Kr and Xe, where deviation from ideality at 300-m depth is -6% and -15% respectively. Taking a linear extrapolation from 300-m depth to the surface (and ideal conditions) for example, would suggest that at 30-m depth Kr and Xe show -0.6% and -1.5% deviation from ideality. Solubility calculations for moderate depth hydrostatic... 

The effect of non-electrolytes such as other dissolved gases in solution is more difficult to assess due to the lack of empirically derived data. Under near surface conditions, most non-electrolytes are relatively insoluble and will have negligible effect. However, at greater pressures significant amounts of major gas species may be in solution. For example at 190atm and 70°C (hydrostatic pressure and temperature at 2km depth), about 3cm sTP) of CH4 saturate 1 cm of pure water to give a 0.13M CH4 solution (Price 1981). The assumption must be made therefore, that interactions between... 

Fig.16 The cationic coordination polymer [[Zn(L)] ] (CFsSOsln a representation of the molecular structme, R = Ph-OH b topographic STM image on HOPG revealing the 1D character imder near-surface conditions. Adapted from [261]...

Although these reports are developed primarily for agricultural purposes, they contain maps with classifications and information on near-surface conditions from investigations that may be useful. In tropical areas, for example, these reports may be essential to obtain dimensions of soft soils such as peat. 

The clays found in sedimentary phosphate rocks include illite, kaolinite, smectites, and magnesium-rich clays such as palygorskite and sepiolite. Illite often appears to be a detrital mineral. Kaolinite, smectites, and magnesium-rich clays often appear to occur in zones within phosphate deposits. This zonation may be related to weathering and the general alteration of deposits under surface or near-surface conditions [15,16]. Clay-Iike minerals such as the zeolite clinoptilolite occasionally are found in phosphate rock. 

Stability of Minerals in Surface and Near-surface Condition... 

Because of these differing conditions, minerals in rocks are transformed to new minerals that are stable at the surface or near-surface conditions. Table 1.4 shows the relative stability of minerals in that environment. 

It is well known that oil and oil refinery products have very high resistivity. However, in near-surface conditions under the impact of oil transforming bacteria during biodegradation the part of soil that is contaminated by oil products becomes a zone of low resistivity. These processes are well studied by geophysicists, biologists and petrochemists. They were additionally modeled in special reactors where... 

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