Groundwater composition

Major constituents (greater than 5 mg/L) Minor constituents (O.Ol-lO.Omg/L) Selected trace constituents (less than 0.1 mg/L) Bicarbonate, calcium, carbonic acid, chloride, magnesium, silicon, sodium, sulfate Boron, carbonate, fluoride, iron, nitrate, potassium, strontium Aluminum, arsenic, barium, bromide, cadmium, chromium, cobalt, copper, gold, iodide, lead, Uthium, manganese, molybdenum, nickel, phosphate, radium, selenium, silver, tin, titanium, uranium, vanadium, zinc, zirconium 

Groundwater may contain dissolved gases as a result of exposure to the surface environment prior water infiltration, contact with the subsurface gaseous phase, and gas produced biologically below the water table. The most important dissolved gas in groundwater is CO.  

Water molecules are built of two elements hydrogen (H) and oxygen (O). The general formula is H20. Different varieties of atoms with different 

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The major terrestrial water reservoirs, the oceans, are well mixed and of rather uniform composition. Upon evaporation, an isotopic separation occurs because the light molecules are more readily evaporated. Thus water in clouds is isotopically light compared to ocean water. Upon condensation, heavier water molecules condense more readily, causing a reversed fractionation. The degree of isotopic fractionation depends on the ambient temperature and other factors which are discussed in Chapter 9. 

Water contains dissolved salts, dissociated into cations (positively charged ions) and anions (negatively charged ions). The most common dissolved cations are sodium (Na+), calcium (Ca2+), magnesium (Mg2+), and potassium (K+). The most common anions are chloride (Cl ), bicarbonate (11 CO,), and sulfate (SO4 ), discussed in section 5.5. The composition of groundwater, that is, the concentration of the different ions, varies over a wide range of values. 

Rocks contain uranium and thorium in small concentrations, and their radioactive decay results in the production of radiogenic helium-4 (4He). The helium reaches the groundwater and is dissolved and stored. With time, 

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Rain in equilibrium with atmospheric C02, but uncontaminated by industrial emissions, should have a pH of 5.7. However, atmospheric pollution from burning fossil fuels has resulted in acid rain of pH as low as 3.5 (24). If this condition continues for a long time, it may lead to a change in groundwater composition, which may considerably change the migration of plutonium in nature. 

Figures 33.3-33.4 show the results at the end of the simulation, after groundwater composition and microbial activity across the aquifer have approached steady state. Once the sulfate initially present is consumed or flushed from the aquifer, the only source of sulfate is in the recharging groundwater. With time in the simulation, sulfate reducing bacteria grow into a community that consumes sulfate from the recharging groundwater and some of the acetate diffusing into the aquifer the acetate and sulfate are consumed in equal molar proportions, according to Reac-...

Fig. 33.3. Steady-state distribution of microbial activity and groundwater composition in an aquifer hosting acetotrophic sulfate reduction and acetoclastic methanogenesis, obtained as the long-term solution to a reactive transport model.

There was a drastic change in groundwater composition from 2004 to 2005. Water within the reduced tailings went from 1 to 800 ppm Fe and 0.2 to 1.3 ppm Zn. The pH values decreased over the same time period from 6.9 to 3.5. 

The establishment of the groundwater composition by the rock and the backfill materials of the repository. 

For slowly moving water deep in rock, the groundwater composition will be established by solubility equilibria. The theoretical knowledge and basic data requirements for these are entirely analogous to those discussed above for dissolution of the wastes. 

Choi, S.-K., Lee, S., Song, Y.-K. Moon, H.-S. 2002. Leaching characteristics of selected Korean fly ashes and its implications for the groundwater composition near the ash disposal mound. Fuel, 81, 1083-1090. 

Lee, S. Spears, D. A. 1995. The long-term weathering of PFA and implications for groundwater composition. Quarterly Journal of Engineering Geology, 28, S1-S16. 

The Groundwater Composition. The composition of the ground-water can be related to (18,19)... 

Groundwater composition in granitic bedrock at great depth and the artificial standard waters used... 

Considering the groundwater composition, you assume that DIPAH+ is mostly competing with monovalent Na+. In this case, use Eq. 11-55 (Box 11.2) to solve for... 

Mobilization of contaminants in Milltown Reservoir can be explained by a model in which groundwater composition is controlled by successive diage-netic reactions during the transition to and from oxic and anoxic environments as the reservoir stage changes (12). Several important reactions govern the mobility of contaminants in this system ... 

Radionuclide transport in natural waters is strongly dependent on sorption, desorption, dissolution, and precipitation processes. The first two sections discuss laboratory investigations of these processes. Descriptions of sorption and desorption behavior of important radionuclides under a wide range of environmental conditions are presented in the first section. Among the sorbents studied are basalt interbed solids, granites, clays, sediments, hydrous oxides, and pure minerals. Effects of redox conditions, groundwater composition and pH on sorption reactions are described. 

The groundwater transport of radionuclides through waterbearing interbed layers in the Columbia River basalt formation will be controlled by reactions of the radionuclides with groundwater and interbed solids. These interactions must be understood to predict possible migration of radionuclides from a proposed radioactive waste repository in basalt. Precipitation and sorption on interbed solids are the principle reactions that retard radionuclide movement in the interbeds. The objective of the work described herein was to determine the sorption and desorption behavior of radionuclides important to safety assessment of a high-level radioactive waste repository in Columbia River basalt. The effects of groundwater composition, redox potential, radionuclide concentration, and temperature on these reactions were determined. 

Procedures. Batch equilibrations of interbed solids (Mabton Interbed, Rattlesnake Ridge sandstone, or tuff), tracers, and groundwaters were used to measure radionuclide distributions between solid and liquid phases. Triplicate measurements were made for each combination of temperature, redox condition, tracer concentration, tracer type, groundwater composition, and interbed sample. Constant temperatures were maintained by placing the... 

Sorption isotherms were also measured for sorption of selenium, technetium, tin, radium, uranium, neptunium, plutonium, and americium on the reference Mabton Interbed solids. The GR-1A groundwater composition was used in these experiments. Two temperatures (23°C 2°C and 60°C 1°C) were used, and both oxidizing and reducing conditions were used for each radionuclide. 

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. 

Effect of Groundwater Composition on Sorption on Magnetite under Anoxic Conditions... 

Sorption on magnetite as a function of groundwater composition shows that, under anoxic conditions, technetium removal from solution is essentially complete after 50 days, with the exception of solutions containing phosphate ions. As pointed out earlier, phosphate was used instead of carbonate, as both are known to form anionic complexes with Tc(IV) (9). In these studies, the presence of humic acid did not affect its sorption. Strong saline solutions (up to 34 000 mg/L Cl) do not have a marked effect on the rate of technetium removal from solution either, as evident from Figure 8. 

Table I. Reference Grande Ronde Groundwater Composition at 25°C ...

Cleveland, J. M. Reese, T. F. Nash, K. L. "Groundwater Composition and Its Relationship to Plutonium Transport Processes Amer. Chem. Soc. Fall Annual Mtg. Kansas City, Sept. 1982, Abstracts of Papers (NUCL 37). 

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