Ground water scenario

Data from chemical characterization were used to estimate possible adverse effects on humans and the environmental receptors. Following previously published works [11, 19], a hypothetic scenario was set up to assess the risk posed by these non-conventional matrix an accidental leachate release into ground-water resulting in 1 100 and 1 1,000 dilutions of the leachate compounds, which have been subjected to dilution as the leachate mixes with the groundwater (Fig. 3). 

Observations The mass transport models can be used to predict best-case and worst-case scenarios of contaminant transport, but in most cases are not exact predictive tools. Both mass transfer and mass transport models are useful to help establish possible contaminant cleanup strategies and, more generally, to help understand the processes that affect the chemical evolution of ground-waters. 

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. 

As stated earlier, the means by which to test a model are dependent on the biases of the model tester and the purposes of his exercise. The purpose of the calibration in this study is to set up the exposure assessment simulations, which will determine the potential for aldicarb to contaminate the ground water in the scenarios modeled. As will be seen shortly, this potential is represented by model results at a point deep in the unsaturated zone. As such, it becomes Imperative to accurately portray aldicarb fate in the unsaturated zone. Since these field studies showed that high concentrations of aldicarb were maintained near the soil surface, parameters were adjusted to portray that behavior. If anything, this exercise has uncovered a discrepancy between model theory and reality, and a future direction in PRZM development and/or field testing might be to test the theories proposed. Nonetheless, the calibration in this study is valid since the purpose is to duplicate reality, given the limitations of the model. 

Figure 2.1 illustrates one of the many possible feedback scenarios. For example, climate changes, mechanical compaction, or heat transport can cause or change ground-water flow. Groundwater flow brings about advection and dispersion of solutes. Mass fluxes across spatial domains cause changes of chemical concentrations, and perturb chemical equilibrium or a chemical steady state, which leads to chemical reactions. 

Depending on the local conditions, a rising water table may be a likely scenario for water entering the pavement structure. An efficient drainage system might save the unbound layers from becoming flooded. Otherwise, ground water will intrude the pavement structure and cause the same effect as the previous scenarios. 

However, in different accident scenarios it is assumed, that ground water may penetrate into the storage field through little crevices in the anhydride layers, which may be part of the salt dome. This water will form saturated, high corrosive salt brines and after corrosion of the storage casks the brines will interact with the fuel elements. A large number of experiments to study the behaviour of HTR fuel elements in such salt brines were performed at the FZ Jiilich starting in the late 70 /5, 6, 7/. A short review of the obtained results is summarised in this chapter. 

Within the task volume activity graphs were designed for each of the elements (in time). Another outputs of the task were maps showing substances concentration at the given sea level. Results obtained (for all the isotopes) were used in radioactive dose calculations. To determine the dose, the scenario of 1 m ground water drunk by a human being a year had been chosen. Based on that scenario ingestion factors were found (SKB 2002) and were stated for all the critical radionuclides shown in Table 3. 

In Table 3 there are shown the maximal volume activities of isotopes on the surface element of the maximal volume activity in the given simulated time. The total dose received by a human with the given scenario (1 m of ground water drunk a year) is calculated out of the volume activities. The other isotopes (not mentioned in Table 3) have lower impact on the given scenario—less 1 pSv. The total dose on other elements is lower (as it is shown in Fig. 4). 

The water demand for enclosed process structures may depend on the degree of compaitmentalization by solid floors and the number of separate systems used to protect the structure. At a minimum, ground floor systems should be assumed to operate in a spill fire scenario. But, if water spray systems are used, it should be assumed that all systems will operate in order to estimate maximum water demand. 

Description of Experiments During the summer of 1980, a series of LNG spill experiments was performed at the Naval Weapons Center (NWC), China Lake, California. The experiments involved eight LNG spills and one liquid nitrogen release (which is not included in the database files) onto a water surface. The release point was in the center of a small pond —58 m in diameter, 1 m deep, with its surface —1.5 m below the surrounding ground level. This was to simulate the accidental release of LNG during an offloading scenario in an aquatic environment where LNG would be spilled onto a water surface. Personnel from NWC and LLNL performed these experiments jointly. 

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