Scenario modeling

The current version of CalTOX (CalTOX4) is an eight-compartment regional and dynamic multimedia fugacity model. CalTOX comprises a multimedia transport and transformation model, multi-pathway exposure scenario models, and add-ins to quantify and evaluate variability and uncertainty. To conduct the sensitivity and uncertainty analyses, all input parameter values are given as distributions, described in terms of mean values and a coefficient of variation, instead of point estimates or plausible upper values. 

H2A delivery scenario model for H2 delivery to urban market (250,000 people). 

H2A delivery scenario model for rural/interstate case. 

A clear decision as to whether the uncertainty is related to the scenario, model or parameters is sometimes difficult. There are, as mentioned, overlaps, and even expert opinions may... 

Each of the three basic sources of uncertainty— scenario , model and parameter —can be further detailed in order to characterize each basic component separately (Table 1). 

An uncertainty analysis gives the assessor the opportunity to re-evaluate the scenario, model approaches and parameters of the analysis and to consider their influence in the overall analysis. The practical impact of uncertainty analysis is illustrated within the annexed case-studies, which also clarify how uncertainty analyses follow a systematic methodology, based on a tiered approach, and consider all possible sources of uncertainty. The first step in uncertainty analysis consists of a screening, followed by a qualitative analysis and two levels of quantitative analysis, using deterministic and probabilistic data. The assessor should be aware that an uncertainty analysis cannot answer all the questions, which, moreover, may lead to new questions. 

Chapter 3 highlighted three basic sources of uncertainty scenario, model and parameter. Methodology for qualitative characterization of uncertainty presented in section 5.1 focuses on these sources. 

Scenario Model High Medium High NA Medium... 

Data, expert judgement or both should be used to inform the specification of uncertainties for scenarios, models and model parameters. 

Lastly, models attempting to predict the fate and resultant exposure to a stressor can be used, and often they are applied in a variety of scenarios. Models, however, are simplifications of our imperfect understanding of exposure and should be tested whenever possible against comparable datasets. The reader should refer to the brief introduction of models found in Chapter 1. 

Table 12.2 Main macroeconomic assumptions in the Polish scenario modelling...

An associated effort is to ensure that the QRA includes the class of events that actually have occurred. Mapping real event scenarios onto scenarios modeled in the QRA allows one to see a particular action integrated into the larger system for each chemical event and thus determine its effect on safety. 

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. 

An extreme iron fertilization scenario modeled by Sarmiento and Orr (1991) relies on the sustained depletion of phosphorus in Southern Ocean surface waters by continuous iron addition. The three-dimensional, multi-layered model predicts a global increase of export production and the possibility of anoxia in deep oceanic waters. Specifically, the results indicate a POC export increase of 6-30 GtCy-1, i.e., a doubling of export production, after 100 years of fertilization. In addition, anoxia is predicted for certain parts of the southwest Indian Ocean. Considering the enormous scale of this hypothesized fertilization operation (0.6Mt utilizable Fey-1 Sarmiento Orr, 1991) and the low spatial resolution of the model, the exercise provides limited insights into more realistic iron fertilization scenarios. 

Goldsmith, P.D. G. Schnitkey. Soybean rust scenario model Crop year 2005 decision-making requires planning. Feedstuffi 2005, 77, March 7. 

Detailed investigation of accident scenarios modeled in Czech PSA projects has led to the conclusion that, at least for major subset of aU actions performed in response to initiating event occurrence and driven by symptom based procedures, lack of time should not be relevant issue. Thus, the time-versus-reliabiUty curves (for short time windows) are used just in some few very special cases of potential lack of time (with time windows shorter than 30 minutes), mostly connected with necessity to recover plant critical safety functions. 

Symptom based procedures can be directly used as the best information source for building of accident scenarios models and accident sequences logic covering the phase of control room crew response to initiating event. According to current requirements, the symptom based procedures set developed for specific plant should cover response to all initiating events defined in plant PSA. 

Figure 2. Evolution of SRRCs, and for the permeability of the plug in the dry scenario (model 6) with the first imputation strategy. 

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