Groundwater solutions

This interface is critically important in many applications, as well as in biological systems. For example, the movement of pollutants tln-ough the enviromnent involves a series of chemical reactions of aqueous groundwater solutions with mineral surfaces. Although the liquid-solid interface has been studied for many years, it is only recently that the tools have been developed for interrogating this interface at the atomic level. This interface is particularly complex, as the interactions of ions dissolved in solution with a surface are affected not only by the surface structure, but also by the solution chemistry and by the effects of the electrical double layer [31]. It has been found, for example, that some surface reconstructions present in UHV persist under solution, while others do not. 

Microbes are ubiquitous in the subsurface environment and as such may play an important role in groundwater solute behavior. Microbes in the subsurface can influence pollutants by solubility enhancement, precipitation, or transformation (biodegradation) of the pollutant species. Microbes in the groundwater can act as colloids or participate in the processes of colloid formation. Bacterial attachment to granular media can be reversible or irreversible and it has been suggested that extracellular enzymes are present in the system. Extracellular exudates (slimes) can be sloughed-off and act to transport sorbed materials [122]. The stimulation of bacterial growth in the subsurface maybe considered as in situ formation of colloids. 

The isotope mass-balance method is not as useful for estimating groundwater-flow rates for groundwater-poor lakes as it is for lakes that receive substantial quantities of groundwater. Solute tracers, such as dissolved calcium, may be useful in assessing... 

Effects of Groundwater Composition and Eh. Radionuclide sorption on geologic solids is dependent on the chemical composition of the groundwater solution and the redox potential (Eh) of the solid-groundwater system. Aquifers at various depths in the Columbia Plateau formation have -been observed to have significant differences in composition. To accurately model radionuclide migration, it is necessary to understand the effects of chemical components and Eh on sorption and solubility of key radionuclides. An additional benefit of this work is to better understand the mechanisms of sorption and desorption of the radionuclides. 

The coupons were contacted with tracer-free groundwater solutions, which were assayed after 28 d to determine the amount of activity that is reversibly bound to the granite under normal groundwater conditions. 

Although selenium is observed in the geologic setting in association with iron, and the DFO model provides a good fit to the groundwater solution data from the dynamic experiments, the selective extraction inventories do not agree well with the model predictions, and the chemistry of selenium is complicated by redox effects (11) It is likely that the DFO model is still too simple to adequately describe selenium migration ... 

Table IV. Major Constituents of the Second Analog Experiment Groundwater Solution in meq/L (Unaltered Basalt) ...

Figure. 7.5. Saturation state of mixtures of groundwater solutions in equilibrium with calcite, at different initial Pc02 values> and seawater at 25°C. (After Plummer, 1975.)...

Wood W. W. and Sanford W. E. (1995) Eolian transport, saline lake basins, and groundwater solutes. Water Resour. Res. 31, 3121-3129. 

Bassett R. L., Buszka P. M., Davidson G. R., and Damaris C.-D. (1995) Identification of groundwater solute sources using boron isotopic composition. Environ. Set Technol. 29, 2915-2922. 

Dissolution of carbonate bedrock by the groundwater solution follows CaC03 + H2CO3 = + 2HCO3. Given that levels of soil CO2 in humid environments are... 

Drake, J.J., and Ford, D.C., 1981, Karst solution a global model for groundwater solute concentrations. Proceedings of the Japanese Geomorphological Union, 2 223-230. 

Many inorganic and organic aqueous species have an influence on As adsorption. The following discussion deals with those elements that are commonly found in groundwater. Solutes can compete directly with As for available surface binding sites and can indirectly influence adsorption by alteration of the electrostatic charge at the solid surface. Both processes are influenced by pH, solute concentration, and the intrinsic binding affinity of the solid (Davis and Kent, 1990). 

We have shown that phytic acid readily hydrolyzes to produce phosphate with a projected lifetime of 100-150 years in the absence of microbiological effects, that actinide-phytate compounds are insoluble, and that europium and uranyl phytates are converted to phosphates within a month at 85 °C. Thorium solubility, on the other hand, is controlled by hydroxide or oxide species. Furthermore, the solubilities of radiotracer europium and uranyl are reduced by phosphate dosing of a simulated groundwater solution, even in the presence of citric acid. In the same systems, neptunium(V) solubility is only affected by 0.01 M phosphate at pH greater than 7. The results of these tracer-scale immobilization experiments indicate that phosphate mineral formation from representative deposits is under thermodynamic control. 

Wu X.Y., Shu L.C. 2006. Groundwater Solute Transport in mining conditions - A Case Study in lining, Shandong (2) 27-30... 

Stalactites and stalagmites are formed by the precipitation of calcium carbonate, CaCOj, when gaseous COj escapes from groundwater solutions. 

In summary, from the above experiments, it can be concluded that the BW30 membrane has a higher rejection of both As and F from synthetic groundwater solution (>90%) than all other membranes tested. NF90, NF270 and SWHR membranes can also be used potentially for removal of both As and F and other ions (except nitrate for NF270). 

Figure 20 Raman spectrum of (top) a standard of magnetite (Fc304) and (bottom) iron particles take from a column that had been treated with simulated groundwater solutions. (Reprinted with permission from MS Odziemkowski, TT Schuhmacher, RW Gillham, EJ Reardon. Mechanism of oxide film formation on iron in simulating groundwater solutions Raman spectroscopic studies. Corros Sci 40 371-389, 1998. Copyright 1998 Elsevier Science.)...

MS Odziemkowski, TT Schuhmacher, RW Gillham, EJ Reardon. Mechanism of oxide film formation on iron in simulating groundwater solutions Raman spectroscopic studies. Corros Sci 40 371-389, 1998. 

Fig. 3. The concentration of some groundwater solutes with time at the locations of the tunnel and boreholes illustrated in Figure 2B A. chloride, B. dissolved iron, C. alkalinity, and D. pH. The sharp dilution front observed in the entrance tunnel at the beginning of the experiment is seen in the plot for chloride. The associated decrease in dissolved Fe was brief and the fracture zone remained anoxic after day 50, as indicated by significant (>0.05 mg 1 ) dissolved iron concentrations throughout the zone.

The ions released during weathering participate in ion exchange equilibria between groundwater solution and adsorption at the surface sites of the mineral phases present. 

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