Hazardous Materials in the Hydrologic Environment The Role of Research by the U.S. Geological Survey (1996) / Chapter Skim
Currently Skimming:
5 Mathematical Models and Decision Support
5 Mathematical Models and Decision Support
Pages 48-69
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 48... ...
In such applications, models can reduce the uncertainty in decision making by providing a rational, self-consistent structure for data collection, site characterization, hypothesis testing, quantification of uncertainty, risk assessment, and the evaluation and design of remediation alternatives (National Research Council, 1992~. Through the years, the USGS has undertaken a spectrum of modeling activities, including those that pertain to contaminant transport and multiphase flow in ground and surface waters (Appe!
|
From page 49... ...
limited to the integration of existing models in decision support systems, the following discussion of predictive models for water quality is largely limited to ground water, whereas the analysis of decision support systems considers both ground water and surface water models. PREDICTIVE WOW AND TRANSPORT MODELS Flow and transport models are now widely utilized and accepted as tools for basic scientific study and management of hazardous materials in surface and ground water environments (Friedman et al., 1984; National Research Council, 199Ob)
|
From page 50... ...
In other areas, such as aquifer analysis, models are used routinely in practice. In terms of overall directions for research, ground water modeling issues with respect to problems of saturated and unsaturated flow in simple porous media therefore do not present the most important challenges.
|
From page 51... ...
Mathematical Models 04 ._ o .e v, ._ ed cd o ~4 co .
|
From page 52... ...
Such efforts would be very useful to Dose working in the area of hazardous waste. Unsaturated Flow in Porous Media Unsaturated flow processes refer to the flow of a single fluid (in this case, water)
|
From page 53... ...
Research is now focused on problems involving dual porosity systems that develop due to the presence of fractures or macropores, and the more complex problem of mass transport through porous media. Although this area of modeling research has not received a high priority within the USGS, there has been work in the development of unsaturated flow and transport codes (e.g., Lappala et al., 1987~.
|
From page 54... ...
However, the U.S EPA is sponsoring the development of simpler sharp interface models for the application to practical problems. The inherent complexity of multiphase models and relatively limited availability of appropriate flow parameters for various materials of interest has unfortunately limited the application of these models.
|
From page 55... ...
and the USGS Cape Cod research site that have provided the most important new insights on field-scale mass transport. Mass transport models are now used routinely to mode} advection and dispersive processes.
|
From page 56... ...
Although considerable research is needed to fully understand the operation of biological systems, some transport models have attempted to include biological effects. The simplest models represent the biotransformation
|
From page 57... ...
Another type of multiphase process is that involving the redistribution of mass among the solids, other liquids, and gases that water encounters in moving through a ground water system. The simplest models of these processes are based on equilibrium mass law relationships for which relatively complete data bases of equilibrium constants are available.
|
From page 58... ...
Progress in the modeling of complex geochemical systems has been much more modest and could be improved to take advantage of the impressive field-scale contributions. Coupled Flow Processes The term "coupled flow" is used to describe interdependent flow and transport processes where, for example, the flow of water depends strongly upon the concentration and/or temperature distributions, and the concentration and/or temperature distributions depend upon the flow of water.
|
From page 59... ...
The main motivation for this work is the importance of fractured media in relation to contamination problems, and the scientific and computational challenges in Me modeling of fractured rock systems. The earliest combined flow and transport models represented fractured systems either as an equivalent porous medium, or as a discrete network of fractures.
|
From page 60... ...
Fracture flow and transport codes are also being used in DOE sponsored studies on both the Waste Isolation Pilot Plant (WIPP) site in New Mexico and the Yucca Mountain site in Nevada.
|
From page 61... ...
This diversification makes sense scientifically and tactically, for it is an imperative to develop new modeling capabilities within the districts as a follow on to the successful Regional Aquifer-System Analysis (RASA) Program.
|
From page 62... ...
input site or watershed data on hydrogeologic characteristics, meteorology, water flow, contaminant sources, and water quality directly or through remote data collection systems; b. access, manipulate, and utilize data files, including those from Geographic Information Systems (GIS)
|
From page 63... ...
Additional development work for decision support systems addressing surface water problems has occurred in selected projects supported by the state water resources institute programs (e.g., Cheng et al., 1993~. In ground water applications, the enormous quantity of site character~zation data at many sites requires that predictive models be interfaced
|
From page 64... ...
, and significant work has been done by private software firms to enhance Me front- and back-end capabilities of the USGS MODFLOW program for more efficient input, output, and parameter estimation. In addition, advanced database management and visualization capabilities have been incorporated into a number of USGS ground water modeling studies.
|
From page 65... ...
They are thus well suited for packages Hat integrate data-base management, modeling, characterization of uncertainty, and visualization of water flow and water quality problems. An important limitation in the application of optimization and decision analysis methods to the management of hazardous materials in the environment is the inherent time lag in incorporation of state-of-the-art process knowledge and models.
|
From page 66... ...
For example, virtually all of the optimization and decision analysis applications to ground water remediation cited earlier were for "pump-and-treat" applications assuming dissolved phase contaminant transport with simple adsorption/reaction processes. In this case, the principal source of uncertainty is assumed to evolve from the stochastic character of the subsurface hydraulic conductivity.
|
From page 67... ...
The DOD contamination hydrology program focuses on specific water and soil quality problems at DOD sites. In most cases, these problems involve subsurface soil and ground water contamination, often with the need to consider geochemical processes for metals and organic complexes.
|
From page 68... ...
To address the evolving needs for advanced process representation, these systems will require flexible configurations to allow new models and data configurations to be imported as the need arises. Decision support systems with data base and modeling capabilities can play a direct and important role in expediting the implementation and interpretation of surface water and ground water studies in both the Federal-State Cooperative and DOD contamination programs.
|
From page 69... ...
The area of decision support is a relatively new field that has not been studied extensively. Opportunities for research exist at the USGS in: · the linkage of powerful visualization technologies with the design of remedial systems; · the creation of decision support "tool-boxes" similar to MMS that would enable users to rapidly create and test decision support systems; and · the integration of mode} and data base capabilities in decision support schemes.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.