Characterization, Modeling, Monitoring, and Remediation of Fractured Rock (2020) / Chapter Skim
Currently Skimming:
1 Introduction
1 Introduction
Pages 9-19
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 9... ...
Because of the discrete nature of transport pathways in fractured rock, approaches applied commonly in soils can be ineffective in fractured rock. Contaminants can be transported great distances and at relatively high velocities along discrete channels, and therefore it becomes necessary to characterize both the rock matrix and properties of fractures that control or affect possible contaminant transport or remediation.
|
From page 10... ...
Monitoring and characterization information is required to identify fracture and matrix porosities, and contaminant fate and transport in both fractures and rock matrix. Uncertainties in characterization data and interpretation can result in inadequate site conceptual models and numerical models of fluid flow and transport.
|
From page 11... ...
Neither does the report include discussion of the infrastructure from which contaminants originate, but rather focuses on their potential impacts to the subsurface geologic and hydrologic environments during the infrastructure lifecycles. The committee includes researchers and practitioners with expertise in areas such as geohydrologic site characterization, hydrogeology, site-scale geotechnical and hydrologic modeling, contaminant fate and transport modeling, geotechnical and geohydrologic monitoring, environmental engineering, remediation practices, and risk assessment (see Appendix A for the committee member biographies)
|
From page 12... ...
PREVIOUS NATIONAL ACADEMIES STUDIES Multiple National Academies studies address issues related to fracture flow, contaminant transport, and subsurface remediation. The report Rock Fractures and Fluid Flow: Contemporary Understanding and Applications reviewed methods and strategies to characterize fracture flow in use from the mid-1970s to the early 1990s (NRC, 1996)
|
From page 13... ...
Fracture geometries can be planar where they form preferentially along or quasi-orthogonal to bedding, as in the relatively undeformed sedimentary rocks pictured in Figure 1.3, but they may be non-planar, as might occur in the folded sedimentary rocks pictured in Figure 1.4. Fracture geometry is a controlling factor of flow: fractures create discrete pathways for both groundwater flow and contaminant transport.
|
From page 14... ...
. The nearly vertical veins and fractures cross cutting the other fractures represent a more recent stress field.
|
From page 15... ...
Dissolved contaminants may react with surrounding geologic materials, precipitate from solution, or exchange electrons or ions with the rock surface and change oxidation states. These reactive dissolved contaminants migrate more slowly than the transporting water and are said to be "retarded" or "attenuated." Some attenuated contaminants -- particularly organic chemicals such as benzene -- tend to be sorbed and held by organic matter found in fractures or by the rock matrix (Zytner, 1994)
|
From page 16... ...
Some radioactive dissolved contaminants such as tritium have a short enough half-life that over a period of a few decades, radioactive decay leads to significant reductions in concentration. Others, such as components of spent nuclear fuels, have half-lives spanning many thousands of years.
|
From page 17... ...
Chemical constituents of fluids in fractures initially diffuse quickly into fluids in the rock matrix surrounding fractures because concentration gradients are high. They diffuse more slowly back into the fractures from the matrix because the gradients are much smaller and are present in two directions (away from and toward the fracture)
|
From page 18... ...
Whereas this report does not include lengthy discussion of research and development in the energy sector, relevant references from that sector are provided throughout this report. REPORT ORGANIZATION This report examines recent progress and addresses issues raised since the publication of the comprehensive 1996 NRC report Rock Fractures and Fluid Flow: Contemporary Understanding and Applications.
|
From page 19... ...
Recommendations in this report are written to improve science, engineering, and research. An integrated systems approach for engineering fractured rock sites is emphasized, so recommendations are presented in a broader systems context.
|
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.