Model contamination modeling

A few of the methods available are applicable to inorganic compounds. These include the PM3/TM method. However, the program is most useful for modeling organic compounds due to a lack of technical features often needed to contend with spin contamination, convergence failure, and so forth. 

Selection of pollution control methods is generally based on the need to control ambient air quaUty in order to achieve compliance with standards for critetia pollutants, or, in the case of nonregulated contaminants, to protect human health and vegetation. There are three elements to a pollution problem a source, a receptor affected by the pollutants, and the transport of pollutants from source to receptor. Modification or elimination of any one of these elements can change the nature of a pollution problem. For instance, tall stacks which disperse effluent modify the transport of pollutants and can thus reduce nearby SO2 deposition from sulfur-containing fossil fuel combustion. Although better dispersion aloft can solve a local problem, if done from numerous sources it can unfortunately cause a regional one, such as the acid rain now evident in the northeastern United States and Canada (see Atmospheric models). References 3—15 discuss atmospheric dilution as a control measure. The better approach, however, is to control emissions at the source. 

In general, the desorptive behavior of contaminated soils and soHds is so variable that the requited thermal treatment conditions are difficult to specify without experimental measurements. Experiments are most easily performed in bench- and pilot-scale faciUties. Full-scale behavior can then be predicted using mathematical models of heat transfer, mass transfer, and chemical kinetics. 

Models for transport distinguish between the unsaturated zone and the saturated zone, that below the water table. There the underground water moves slowly through the sod or rock according to porosity and gradient, or the extent of fractures. A retardation effect slows the motion of contaminant by large factors in the case of heavy metals. For low level waste, a variety of dose calculations are made for direct and indirect human body uptake of water. Performance assessment methodology is described in Reference 22. 

Y. S. Sedunov, V. A. Borzilov, and N. V. Klepikova, Use of Mathematical Modeling to Estimate Formation of Contaminated Areas Resultingfrom Nuclear Accident, IAEA-SM-306/114, IAEA, Vienna, Austria, 1990. 

An extensive pesticide properties database was compiled, which includes six physical properties, ie, solubiUty, half-life, soil sorption, vapor pressure, acid pR and base pR for about 240 compounds (4). Because not all of the properties have been measured for all pesticides, some values had to be estimated. By early 1995, the Agricultural Research Service (ARS) had developed a computerized pesticide property database containing 17 physical properties for 330 pesticide compounds. The primary user of these data has been the USDA s Natural Resources Conservation Service (formerly the Soil Conservation Service) for leaching models to advise farmers on any combination of soil and pesticide properties that could potentially lead to substantial groundwater contamination. 

Fiend s Constant. Henry s law for dilute concentrations of contaminants ia water is often appropriate for modeling vapor—Hquid equiHbrium (VLE) behavior (47). At very low concentrations, a chemical s Henry s constant is equal to the product of its activity coefficient and vapor pressure (3,10,48). Activity coefficient models can provide estimated values of infinite dilution activity coefficients for calculating Henry s constants as a function of temperature (35—39,49). 

Establishing the physical and analytical boundaries for a QRA is also a difficult task. Even though you will provide input, the scope definition will largely be made by the QRA project team. Defining the physical boundaries is relatively straightforward, but it does force the QRA team to explicitly identify and account for interfaces that may significantly affect the QRA results. Eor example, analysts often treat a connection to a power supply (e.g., a plug) or a feed source as a physical boundary yet, loss of power or contamination of the feed must be considered in the QRA model. 

Similarly, contaminant concentrations in rivers or streams can be roughly assessed based on rate of contaminant introduction and dilution volumes. Estuary or impoundment concentration regimes are highly dependent on the transport mechanisms enumerated. Contaminants may be localized and remain concentrated or may disperse rapidly and become diluted to insignificant levels. The conservative approach is to conduct a more in-depth assessment and use model results or survey data as a basis for determining contaminant concentration levels. 

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

If the hypothesis or model does not seem to be a good predictor of what is happening in the building, you probably need to collect more information about the occupants, HVAC system, pollutant pathways, or contaminant sources. Under some circumstances, detailed or sophisticated measurements of pollutant concentrations or ventilation quantities may be required. Outside assistance may be needed if repeated efforts fail to produce a successful hypothesis or if the information required calls for instruments and procedures that are not available in-house. Analysis of the information collected during the LAQ investigation could produce any of the following results ... 

Detailed sampling can include, but is not limited to, the installation of monitoring well networks. After the wells have been installed, aquifer tests are typically performed. Once the aquifer tests are performed and the aquifer characteristics are determined, time series sampling for a given contaminant, or a surrogate, is undertaken. The combined results of these efforts provide the basis for development of a treatment strategy. Modeling can be used as part of this effort to help determine the best technical and most cost-effective techniques to be used at a site. 

Mathematical predictive modeling based on predictive equations. Analogous chemical structures. Employers would rely on service life values from other chemicals having analogous chemical structure to the contaminant under evaluation for breakthrough. 

This chapter describes the aerodynamic principles, models, and equations that govern the flow and the contaminant presence and transport in a designated volume of a work room. The purpose of local ventilation is to control the transport of contaminants at or near the source of emission, thus minimizing the contaminants in the workplace air. 

This chapter describes calculation models for building energy demand and air flow in and around industrial buildings. Special attention is paid to simulation of airborne contaminant control. 

The target level procedure was applied to 16 common air contaminants (Table 6.19). These are common contaminants in the industrial environment, and in many cases are the most critical compounds from the viewpoint of need for control measures. The prevailing concentration data as well as the benchmark levels were taken from Nordic databases, mainly the Finnish sources, and described elsewhere.In addition, a general model for assessing target values for other contaminants is presented in the table. 

General model ior other contaminants <0.1 xOEI 0.1 xOfI.ro 0.2.5 xOTL [Pg.403]

An alternative simple model for contaminant dilution of rooftop exhaust stacks is presented in Halitsky. This model combines a jet region specification for the upward exhaust movement with a more traditional Gaussian plume region controlled by atmospheric and building-generated turbulent dilution. 

The following equations separately outline calculating contaminant concentration inside a room with central and local recirculation. The assumptions for the room are that it has one main ventilation system with supply and exhaust air and that the contaminant concentration is the same in the whole volume (except very close to the contaminant source or in the ducts, etc.). The contaminant source is steady and continuous. The model for local ventilation assumes also one main ventilation system to which is added one local exhaust hood connected to a local ventilation system (see Chapter 10) from which all the air is recirculated. In the central system the number of inlets and outlets could vary. The flow rates are continuous and steady. 

FIGURE 8.1 Model of a central recirculating system used for calculating the connection between contaminant concentrations, airflow rates, contaminant source strength, q, and air cleaner efficiency, rj. Cj p is the concentration in the supply (outside) air, c is the concentration in the room, c is the concentration in the returned air, (JaMot the total flow rate through the room, ic is the ratio between recirculated airflow rate and total air flow rate, T is the time constant for the room, and V is the room volume. 

One of the most common systems for cleaning air in homes, offices, schools, etc. is the room air cleaner. Figure 8.2 outlines a model of a local recirculating system. Usually these units are situated inside the room if they are small and movable (see Chapter 10). For the model it does not matter if the unit is placed inside or outside the room with the contaminant source, as long as the exhaust and return air openings are inside. 

Local ventilation in industry usually differs from the description above in that it is connected to a local exhaust hood (Chapter 10), which has a capture efficiency less than 100%. The capture efficiency is defined as the amount of contaminants captured by the exhaust hood per time divided by the amount of contaminants generated per each time (see Section 10.5). Figure 8.3 outlines a model for a recirculation system with a specific exhaust hood. Here, the whole system could be situated inside the workroom as one unit or made up of separate units connected with tubes, with some parts outside the workroom. For the calculation model it makes no difference as long as the exhaust hood and the return air supply are inside the room. 

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