Research Needs in Subsurface Science (2000) / Chapter Skim
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5 Knowledge Gaps and Research Needs
5 Knowledge Gaps and Research Needs
Pages 93-114
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From page 93... ...
Rather, the committee has focused on the identification of the knowledge gaps that underpin those technology gaps. The committee has been selective in the identification of subsurface contamination knowledge gaps and research needs for the EM Science Program.
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From page 94... ...
Organizing Scheme Used in This Analysis The committee identified significant knowledge gaps and research needs through discussions and analyses of the "snapshot" of DOE's subsurface contamination problems presented in Chapter 2. To organize this analysis and ensure its completeness, the committee developed the organizing scheme shown in Figure 5.1.
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From page 95... ...
This step involves determining the spatial distributions, types, amounts, and physical and chemical states of subsurface contaminants, as well as the subsurface properties that affect contaminant fate and transport behavior. Locating and characterizing contamination in the subsurface may be done using direct (e.g., drilling and sampling)
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From page 96... ...
The predictive model can be used to understand the present behavior of the subsurface system and to estimate future contaminant migration to assess risk to human and environmental health (Box 5~. A corrective action decision (Box 6A-E)
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From page 97... ...
Knowledge Gaps The committee identified significant knowledge gaps in the following process steps in the framework for site remediation shown in Figure 5.1: location and characterization of subsurface contaminants and characterization of the subsurface (Box 1~; conceptual modeling (Box 2~; containment and stabilization (Box 6B) ; and · monitoring and validation (Boxes 4 and 7 and Arrows 1 and 2~.
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From page 98... ...
The challenges of locating subsurface contamination are magnified by the wide range of contaminant types (e.g., mixtures of organic solvents, metals, and radionuclides) in the subsurface at many DOE sites (see Chapter 2~; the wide variety of geological and hydrological conditions across the DOE complex (see Table 2.2~; and the wide range of spatial resolutions at which this contamination must be located and characterized, ranging from widely dispersed contamination in groundwater plumes to small isolated hot spots in waste burial grounds.
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From page 99... ...
Moreover, research on subsurface heterogeneity in geology, geochemistry, hydrology, and microbiology will provide a framework for assessing the fate and transport of contaminants. Examples of significant knowledge gaps include the following: · Locating contaminants in the subsurface.
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From page 100... ...
Subsurface characteristics also govern the selection of conceptual and predictive models as well as the application and effectiveness of appropriate corrective actions. The knowledge gaps include understanding which characteristics control fate and transport behavior in the subsurface and also understanding how those characteristics can be measured at the appropriate scales over large subsurface volumes, using both indirect and direct techniques.
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From page 101... ...
These approaches should provide information on the following system properties and behaviors at the spatial and temporal scales that control contaminant fate and transport behavior: · contaminant locations and characteristics: · transport pathways; · subsurface properties and boundary conditions that control contaminant fate and transport behavior; and · physical, chemical, and biological interactions between contaminants and earth materials. SIDEBAR 5.1 NEW APPROACHES FOR DIRECT OBSERVING The major limitations on direct observations by conventional drilling and sampling have been high costs and concerns that direct approaches may unwittingly exacerbate the spread of contaminants in the subsurface.The use of reduced diameter driliholes (using 4- to 6-inch diameter drills)
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From page 102... ...
Conceptual and predictive models have been developed for subsurface contaminant fate and transport for many DOE sites, but in many cases these models have proven ineffective for understanding and predicting contaminant movement, especially at sites that have thick unsaturated zones or complex subsurface characteristics. The conceptual model "problem" has many possible causes.
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From page 103... ...
Understanding the dominant contaminant transport processes and pathways through the subsurface remains a significant knowledge gap for building accurate and useful conceptual and predictive models. The simplest formu ration of contaminant transport uses porous media flow of a dissolved phase, but such transport may be the exception at many DOE sites, where transport can occur in several distinct manners (e.g., colloidal transport)
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From page 104... ...
The definition and estimation of model parameters requires a good understanding of the subsurface system and transport processes being modeled, which is not often the case at DOE sites. For example, the traditional approach for modeling porous media is to choose permeability as a model parameter.
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From page 105... ...
The knowledge gaps include understanding the scale effects and developing methods for data integration that take these effects into account. Research Needs Conceptual model development has not been an explicit topic for basic research in its own right.
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From page 106... ...
The committee provides additional comments on this issue in the next chapter.6 Containment antl Stabilization As noted by DOE in Paths to Closure (DOE, 1 998a) and as shown in Chapter 2 of this report, a great deal of subsurface contamination is likely to remain at DOE sites even after DOE's cleanup program is completed.
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From page 107... ...
The committee believes that the significant knowledge gaps include the following: · Development of robust physical, chemical, and biological containment and stabilization systems. Trad itional contai n ment systems comprised of surface caps, in situ walls, and bottom barriers employ low-permeability materials to reduce water infiltration and provide a barrier to contaminant migration.
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From page 108... ...
work well in humid environments, but they may not be effective in arid regions, where dessication can lead to the development of preferred pathways. To the committee's knowledge, there has been little or no research or development work on longer-term systems for containment of subsurface contamination of the sort encountered at DOE sites, either by DOE or by other organizations.9 The knowledge gaps include understanding how to design more effective and permanent barrier systems for long-term containment, especially in arid environments characteristic of the western DOE sites, including the development and application of more durable materials for barrier systems materials that are compatible with the surrounding environment and with the waste that is being contained.
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From page 109... ...
Monitoring and Validation The abi I ity to man itor and val idate is essential to the successfu I application of any corrective action to a subsurface contamination problem, as is regulatory acceptance of that action. However, the knowledge and technology bases to support these activities are not fully developed and are receiving little attention in EM's science and technology programs.
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From page 110... ...
At the front end, monitoring and validation are used to support the development of conceptual and predictive models of subsurface and contaminant behavior (Box 4 and Arrow 1~. At the back end, monitoring and validation are used to gain regulatory acceptance for corrective actions and to demonstrate the effectiveness of efforts to remove, treat, or especially to contain contamination (Box 7 and Arrow 2~.
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From page 111... ...
The issues here are simi lar to those for model validation, that is, how to assess whether the process is performing as designed. The knowledge gaps include understanding what to measure, how to measure it, how to assess discrepancies between designed and measured behavior, and determining what diagnostic information these differences provide for assessing and improving performance.
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From page 112... ...
how to validate the future performance of the model or system behavior based on present-day measurements. These questions might be addressed through research projects that focus on the development of validation methodologies using real-world examples at DOE sites.
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From page 113... ...
and indirect (e.g., using plants and animals) measurements over long time periods, particularly for harsh chemical environments characteristic of some DOE sites.
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From page 114... ...
Indeed, the list of knowledge gaps presented in this chapter is not exhaustive and is perhaps notable for what it does not include, namely, the knowledge gaps associated with assessment of risk (Box 5 in Figure 5.1~° and many of the corrective actions associated with EM's cleanup program (Boxes 6C through BE in Figure 5.1~. The committee has been selective because (1 )
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