Leaching scenarios

Figure 5. Development of U concentration profiles during a leaching scenario, D/R=10. Here diffusive uptake occurs for 10 ky at a relative groundwater concentration of 10 after which the concentration is dropped to 1. U is lost initially from the outer portions of the bone, leading to distinctive M- and n-shaped profiles. [Used by permission of Elsevier Science, from Pike et al. (2002), Geochim Cosmochim Acta, Vol. 66, Fig. 3f, p. 4276.]...

Figure 6. Development of date profiles during the leaching scenario = 1.0). Because U but not...

Chemical degradation rate, soil permeability and rainfall are primary drivers for deciding leaching scenarios ... 

TABLE 22.1 Overview of the Characteristics of the Nine Leaching Scenarios... 

Leaching processes introduce hydrocarbon into the water phase by solubility and entrainment. Leaching processes of petroleum products in soils can have a variety of potential scenarios. Part of the aromatic fraction of a petroleum spill in soil may partition into water that has been in contact with the contamination. 

Waste form leach rates in a geologic repository will be affected by unknown water flow rates and by extensive cracking of the waste form monolith. An understanding of these effects is important in predicting the geochemical behavior of disposed radioactive waste forms over the full range of possible scenarios. The dependence of the waste form source term on the rate of renewal of aqueous solution is first established for the simple but important case of solubility-limited network dissolution control. 

Briefly recalled, the WASTOXHAS approach consists in characterizing the ecotoxicological hazard potential of contaminant fluxes from waste leachate obtained under defined conditions with two different dynamic leaching procedures laboratory simulated leaching tests and field leaching tests. The approach developed below considered a specific scenario that simulates a waste deposit receiving rain or run-off water (Perrodin et al., 2002). 

The characterization of leaching behavior in water of solidified/stabilized waste is crucial in most reuse or disposal scenarios. Water plays a multiple role in physico-chemical phenomena in the solid, in pollutant transfer and pollutant dispersion in the environment. 

The pollutant flux due to leaching depends on the physico-chemical mechanisms which govern mass transfer when solidified/stabilized waste comes into contact with water in the scenario conditions. The use of hydraulic binders has several effects on the leaching behavior of pollutants (mainly metallic species) including [22] ... 

However, the relative importance of scenarios has been yet been recognized in what may be termed the validation of generic exposure assessments such as examining the leaching potential of a compound in the EU using the FOCUS groundwater scenarios [20] or running US EPA s standard scenarios for runoff and drift [25]. 

In safety assessments, the following scenario is discussed access of water, corrosion of the containers, leaching of the waste and migration of the radionuclides to upper layers of the earth where they may enter the biosphere. 

Batchwise kinetic leaching is aimed at understanding both the rate and extent of TE remobilization by changes in environmental scenarios. Moreover, this tecluiique has the potential to overcome the recognized limitation of phase overlapping of several extractants (e.g., the single and sequential extractants of SM T procedures) whenever the several pools attacked feature different kinetic behavior. Contributions of readsorption phenomena to the thermodynamic leachate results may also be discerned by evaluation of kinetic data (Bermond et al., 1998). Manual fractionation protocols based on kinetic explorations are capable of... 

The purpose of this paper is to present an assessment exercise of a leaching pesticide using the PRZM model. The assessment begins with a calibration of PRZM for the pesticide aldicarb applied to tobacco in North Carolina and potatoes in Wisconsin. Following these calibrations, long term simulations are performed using these same calibration scenarios. Examination of key PRZM output indicates the "potential" for aldicarb to contaminate ground water in the scenarios modeled. 

---