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Modeling the behavior of contaminants in a subsurface flow is important in predicting the fate of the pollutants, in risk assessment, and as a preliminary step of the mitigation process. A two-dimensional transport model with advection and dispersion is used as the deterministic model of a conservative contaminant transport in the subsurface. With the system model alone, it is very difficult to predict the true dynamic state of the pollutant. Therefore, observation data are needed to guide the deterministic system model to assimilate the true state of the contaminant. Extended Kalman Filter (EKF), which is essentially a first order approximation to an infinite dimensional problem, is used in this study to predict the contaminant plume transport. A traditional root mean square error (RMSE) of pollutant concentrations is used to examine the effectiveness of the EKF in contaminant transport modeling. The result shows that EKF can reduce 74 to 91% of prediction errors compared to the numerical method while working with the full set of observation data and using the analytical solution as the true solution. It can reduce 24 to 90% of prediction errors while working with only 2.25% observation-site data and a simulated random true field. DOI: 10.1061/(ASCE)EE.1943-7870.0000179 CE Database subject headings: Stochastic processes; Pollutants; Kalman filters. Author keywords: Stochastic process; Dynamic system; Contaminant transport; Process noise; Observation noise; Extended Kalman filter (EKF).

Buildup/wash-off (BUWO) models are widely used to estimate pollutant export from urban and suburban watersheds. Here, we propose that the mass of washed-off particulate during a storm event is insensitive to the time between storm events (the traditional predictor of particulate accumulation in BUWO models). Our analysis employed USGS data of total suspended solids and discharge data for nonsnow events in a 9.4-[km.sup.2] suburban catchment in Madison, Wis. Kinetic energy of rainfall was calculated using National Weather Service NEXRAD radar reflectivity. A regression analysis found that storm event runoff volume and rainfall kinetic energy explained 81% of the variability in event particulate load; volume alone explained 69% of the variability in event loads. Time between storm events was not significant. Additionally, we simulated storm event particulate loads using a BUWO model and a model assuming a constant mass available for wash-off. Both models produced very similar predictions over a range of parameterizations, suggesting that buildup models could perhaps be simplified under many circumstances. DOI: 10.1061/(ASCE)EE.1943-7870.0000142 CE Database subject headings: Watersheds; Water pollution; Surface water: Stormwater management; Urban areas; Wisconsin; Catchments. Author keywords: Nonpoint source pollution; Urban hydrology; Buildup/wash-off models; Nexrad Levell II Data.

Byline: Andreas Lange (1,2), Ulf Moslener (2,2) Keywords: pollutant interaction; uncertainty and learning; new technologies Abstract: We analyze the problem of introducing a new substitute for a polluting process. The environmental effects of this substitute are uncertain but will be resolved over time. In a two-period model where two stock pollutants are substitutes in the abatement cost function, we show that the consequences of uncertainty depend critically on the degree of substitutability. As opposed to independent pollutants, for potentially large damages a further increased level of uncertainty leads to a decrease in risky emissions at the expense of emitting more of the old pollutant with known environmental effects. We illustrate how the effects of revealed uncertainty on the emission levels are affected by increasing substitutability. Author Affiliation: (1) Centre for European Economic Research (ZEW), P.O. Box 103443, 68034, Mannheim, Germany (2) Interdisciplinary Institute for Environmental Economics, University of Heidelberg, Bergheimer Str. 20, 69115, Heidelberg, Germany Article History: Registration Date: 02/10/2004

Transport of contaminant through a single fracture, modeled as a closely spaced parallel plates aperture, is analyzed theoretically and numerically. Permeable contact regions between the plates are modeled as fixed packs of homogeneous, isotropic, and inert porous material. A nondimensional theoretical expression for estimating the equivalent global permeability of the aperture is presented in terms of the relative volume occupied by the contact regions. Transient transport of contaminant (solute) through this heterogeneous system is analyzed considering injection of fluid with uniform concentration at the inlet of the fracture. For natural systems, it is verified that relative volume and distribution of contact regions affect clean-up time, defined as the time necessary for the complete removal of contaminant, only indirectly by yawing the equivalent permeability of the system, otherwise their effect is negligible. The clean-up time of a clear (of contact regions)fracture, is correlated with the Peclet number for [10.sup.-1] [less than or equal to] Pe [less than or equal to] [10.sup.6].

A numerical method is developed to minimize the environmental impact of one or multiple contaminant point sources in a vertically mixed river or estuary. The algorithm is based on a finite-element solution of the adjoint to the fate and transport equation that permits efficient selection of optimal locations and mass loadings of outfalls in the presence of tidal action, secondary currents, river branches, and other two-dimensional factors. The evaluation is based on the cumulative effects of contaminants in one or more arbitrary target points in the system. The model is validated by comparison to repeated trial solutions and is shown to yield information comparable to that resulting from a large number of hypothetical simulations. Practical applications are presented for the Fox River and the upper Potomac Estuary verifying the method's applicability to rivers of arbitrary geometry and bathymetry.

An existing two-dimensional estuary model was modified to incorporate processes important to the transport and fate of copper in San Francisco Bay. These processes include advection, dispersion, partitioning with suspended particles, settling, and resuspension of adsorbed copper. A systematic calibration of these processes was made. The simulated advection was first shown to match tidal stages, time lag of slack waters, and currents. The model's dispersion was then calibrated by matching observed total dissolved solids. Finally, the model was calibrated to match total suspended solids, total copper, dissolved copper, and sediment copper. The model simulated the recently observed copper concentration in the bay under current point and nonpoint source loadings. The model predicted that a reduction of copper load in winter storm-water runoff would lower copper concentration in the summer.

Introduction Unconfined aquifers constitute valuable and renewable water resources that can be exploited at minimal cost. In situations where the water table is close to ground surface, exploitation costs are [...]

Byline: M.C. Cirillo, G. Graziani Since the (partial) acceptance in Italy of the EU Directive 85/337/EEC concerning environmental impact assessment procedures, there has been a rapid growth in the use of atmospheric dispersion simulation tools, which are also being used in air-quality management plans. This paper describes the state of the art in the development and application in Italy of the short and medium range atmospheric models, limiting the analysis to deterministic and to inert (or linear chemistry) pollutants models. A number of software packages capable of describing the concentration and dose field using analytical solutions of the advection diffusion equation exist, and they have been thoroughly used and compared with a number of field data. Among these, a brief description of DIMULA (ENEA), APC-2 (ENEL), AMETISTA (ANPA), KAPPAG (CNR) and MRBT is given. A puff model (AVACTA) is also described that takes into account the spatial and temporal variability of average wind and turbulence for rough terrain, since it was partly developed in Italy where it is extensively applied. More recently, efforts have been made by different groups in the development and assessment of Lagrangian particle models for complex terrain. They are based on the solution of the Langevin equation and are usually coupled with the output of 3-D prognostic or diagnostic flow models for the calculation of particle trajectories. Descriptions are given of ARCO (ANPA), SPRAY (ENEL-CNR) and MONTECARLO (JRC-Ispra) together with a comparison of their results with some short and mesoscale field experiments. There is at present no list of officially approved models for regulatory purposes in Italy, The recent decision to establish the Italian Environment Agency (ANPA) indicates that this important issue will soon be considered.

Byline: Viktor V. Pocajt, Radmila S. Cvijovic A complex expert system for air pollutant dispersion modeling (ScalEx) is currently being developed at Faculty of Technology and Metallurgy in Belgrade. The project goal is to develop a powerful software system as an engineering toolbox for modelling air pollutant dispersion under various conditions and terrain configurations. ScalEx is planned to be an integrated software system of the new generation, putting together an expert system, advanced database technologies, hypermedia, conventional numeric routines and neural networks.

The Dutch National Model was revised during 1995 and 1996 in a task group consisting of representatives of the relevant institutes and universities in the Netherlands. The advanced model 'STACKS' was chosen as the model of departure. From an evaluation some modifications were agreed, in particular for the surface layer and the treatment of directional wind shear in the model. The resulting Reference Model will serve as a calibration standard for a simplified version meant for regulatory purposes.

Byline: J. Gotting, Ch. Winkler, M. Rau, N. Moussiopoulos, G. Ernst The three-dimensional microscale numerical model MIMO was applied to calculate the dispersion of a passive pollutant in the vicinity of a U-shaped building. Three different locations of a non-buoyant source and six different wind directions were examined. The calculated concentrations were compared with concentrations measured in a boundary layer wind tunnel. The comparison shows a very good agreement between numerical and wind tunnel results.

Byline: P. Kassomenos, S. Lykoudis, M. Petrakis The main features that characterise the Athens Metropolitan Area (AMA) are its geographical position in the Attic Peninsula, the complicated topography and the neighbouring industrial zone, located to the west and separated from the AMA by a hilly area. The transport of air pollutants from this zone to Athens has been the subject of a number of theoretical and experimental studies. In this paper, using the meteorological and dispersion modelling system EZM, the vertical distribution of air pollutants, released from a number of stacks of various types and characteristics, and transported over Athens, was simulated and discussed. It was found that the vertical distribution mainly depends on the physical height of the stacks.