Contaminant transport

Monitoring Well Design for Contaminant Transport Studies... 

Nonaqueous phase Hquids (NAPLs) present special problems for soil and ground water cleanup. Contaminant transport through ground water depends in part on the water solubiHty of the compound. Because NAPLs cling to subsurface particles and are slow to dissolve in ground water, they hinder cleanups and prolong cleanup times. Dense nonaqueous phase Hquids (DNAPLs) migrate downward in the aquifer and can coUect in pools or pockets of the substmcture. Examples of DNAPLs are the common solvents tetrachloroethylene (PCE) and trichloroethylene (TCE) which were used extensively at many faciHties before the extent of subsurface contamination problems was realized. 

FIGURE 10.6 Definition of capture efficiency, a, M = contaminant source rate, m = contaminant transport (directly) into the exhaust hood, a — m/M. 

The inlet opening that supplies the low-momentum airflow should be sufficiently wide to cover the contaminant source and should face toward the inlet of exterior hood. The airflow functions to transport contaminants emitted within the flow to the exterior hood. The exhaust airflow created around the suction opening must exhaust all of the contaminants transported by the supplied airflow. From this point of view, the low-momentum... 

An established design method for this type of system is not available. The practical design of the low-momentum supply with exterior hood system described in the previous part of this section used the flow ratio method. How-evec, the actual exhaust flow rate was adjusted visually to the appropriate value in order to exhaust only the contaminants transported by the supply airflow. 

The humidity and contaminant transport calculation is based on the previously calculated airflows, applying again the principle of mass conservation for the species under consideration. For each time step, the concentrations are calculated on the basis of the airflows, the source and sink strengths in the zones, and the concentration values at the previous time step. In contrast to the airflow calculation, which is a steady-state calculation at each time step, the contaminant transport calculation is dynamic. Therefore, the accuracy of the concentration results depends on the selected time-step interval. 

Zone humidity (if humidity is not considered as species in the contaminant transport calculation)... 

The integration of the ventilation model into the thermal building model can be realized on different levels, from simple stack-flow equations to a full integration of a multizone airflow and contaminant transport model. 

Equations (12.40) to (12.45) describe the velocities u, v, w, the temperature distribution T, the concentration distribution c (mass of gas per unit ma.ss of mixture, particles per volume, droplet number density, etc.) and pressure distribution p. These variables can also be used for the calculation of air volume flow, convective air movement, and contaminant transport. 

Experiments on the scale of 1 to 1 are often used to study the local ventilation around an operator s workplace. Tracer gas is used to simulate the contaminant transport, and a high concentration level of the model tracer gas makes it possible to work with a convenient level of concentration for the measurements. Figure 12.31 shows an enclosure with an emission source S and a laboratory. setup with a model source 5,. The dimensionless concentration c/cg is... 

Crosswise Airflow that takes place from one side of a space to the other. This may be achieved by one or more jets or by allowing the air to enter the whole of one side surface and extracting the air by the whole area of the opposite side. The latter arrangement provides a piston effect, ensuring good air and contaminant transport. 

Alexander WR, McKinley IG (1994) Constraints on the use of in situ distribution coefficients (Kd) values in contaminant transport modeling. Eclogae Geol Helv 87 321-324 Andrews JN, Wood DF (1972) Mechanism of radon release in rock matrices and entry into groundwaters. Inst Min Metall Trans B81 198-209... 

Falta, R.W., Pruess, K. and Chestnut, D.A., Modeling advective contaminant transport during soil vapor extraction, Ground Water, 31, 1011-1020, 1993. 

Data analysis should focus on the development or refinement of the conceptual site model by analyzing data on source characteristics, the nature and extent of contamination, the contaminants transport pathways and fate, and the effects on human health and the environment. All field activities, sample management and tracking, and document control and inventory should be well managed and documented to ensure their quality, validity, and consistency. 

This section discusses soil liners and their use in hazardous waste landfills. The section focuses primarily on hydraulic conductivity testing, both in the laboratory and in the field. It also covers materials used to construct soil liners, mechanisms of contaminant transport through soil liners, and the effects of chemicals and waste leachates on compacted soil liners. 

Onishi, Y. Wise, S.E. "Mathematical Model, SERATRA, for Sediment - Contaminant Transport in Rivers and its Application to Pesticide Transport in Four Mile and Wolf Creeks in Iowa EPA-600/3-82-045, U.S. Environ. Prot. Agency, Environ. Research Lab. Athens, Georgia,1982 p. 56. 

Schwartz, F.W., A. Growe (1980). A deterministic probabilistic model for contaminant transport, US NRC, NUREG/CR-1609, Washington, DC. 

Zheng, C. and G. D. Bennett, 2002, Applied Contaminant Transport Modeling, 2nd ed. Wiley, New York. 

Surface tension is responsible for capillary effects and spreading of the NAPL over the water table. At about 20°C, water has a surface tension of 73.05 dyn/cm, whereas CC14 has a surface tension of only 26.95 dyn/cm. Therefore, water will be held in an unsaturated porous media by surface tension to a much greater degree relative to carbon tetrachloride (i.e., the permeability of porous media will be different with respect to each liquid). The ramifications will be important for contaminant transport of mixed wastes. 

Corapcioglu, M. Y. and Baehr, A. L., 1985, Immiscible Contaminant Transport in Soils and Groundwater with an Emphasis on Gasoline Hydrocarbons System of Differential Equations vs. Single Cell Model Water Science and Technology, Vol. 17, No. 9, pp. 23-37. 

An important and recently reported issue, namely slow sorption/desorption rates, their causes at the intra-particle level of various solid phases, and how these phenomena relate to contaminant transport, bio availability, and remediation, is also discussed and evaluated. A case study showing the environmental impact of solid waste materials which are mainly complex organic mixtures and/or their reuse/recycling as highway construction and repair materials is presented and evaluated from the point of view of sorption/desorption behavior and data modeling. 

Generally, slow sorption or desorption has made complete remediation technology difficult. However, there have recently been legitimate questions raised by some researchers [163,187] about whether we even need to be concerned about residues that desorb so slowly and thus are apparently largely bio-unavailable. At a minimum, it is important that we understand the factors which govern slow sorption/desorption rates, their kinetics and causes at the intra-particle level of different solid phase materials (e.g., surface/subsurface and aquatic sediment particles), and how these phenomena can relate to contaminant transport, bioavailability, toxicity, remediation, and risk assessment modeling. 

Simulation and predictive modeling of contaminant transport in the environment are only as good as the data input used in these models. Field methods differ from laboratory methods in that an increase in the scale of measurement relative to most laboratory methods is involved. Determination of transport parameters (i. e., transmission coefficients) must also use actual contaminant chemical species and field solid phase samples if realistic values are to be specified for the transport models. The choice of type of test, e.g., leaching cells and diffusion tests, depends on personal preference and availability of material. No test is significantly better than another. Most of the tests for diffusion evaluation are flawed to a certain extent. 

Wilson and Madsen [152] used the metabolic pathway for bacterial naphthalene oxidation as a guide for selecting l,2-dihydroxy-l,2-dihydronaphthalene as a unique transient intermediary metabolite whose presence in samples from a contaminated field site would indicate active in situ naphthalene biodegradation (Fig. 26). Naphthalene is a component of a variety of pollutant mixtures. It is the major constituent of coal tar [345], the pure compound was commonly used as a moth repellant and insecticide [345], and it is a predominant constituent of the fraction of crude oil used to produce diesel and jet fuels [346]. Prior studies at a coal tar-contaminated field site have focused upon contaminant transport [10,347], the presence of naphthalene catabolic genes [348, 349], and non-metabolite-based in situ contaminant biodegradation [343]. 

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