Characterization, Modeling, Monitoring, and Remediation of Fractured Rock (2020) / Chapter Skim
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6 Remediation of Fractured Rock
6 Remediation of Fractured Rock
Pages 94-111
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From page 94... ...
The majority of technologies developed for porous media remediation are not applicable in fractured rock settings (NRC, 1994; SERDP, 2001) , and the time frames for remediation can be longer than estimated for unconsolidated porous media sites (without significant contaminant storage)
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From page 95... ...
is inherently faulty, although that limitation may not be recognized by all appropriate parties. DIFFICULTIES OF REMEDIATION IN FRACTURED ROCK Characterization As discussed in Chapter 5, the level of detail in characterization required for remediation of fractured rock sites exceeds significantly that required at most unconsolidated media sites and may not be possible given budgetary and technology limitations.
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From page 96... ...
. Remediation approaches such as conductive heating can be rendered ineffective if a single highly transmissive fracture is not detected during characterization.
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From page 97... ...
The combination of these processes, in conjunction with the difficulty identifying plume centerlines, often results in plumes in fractured bedrock being described as "dilute" or "diffuse." Treatment approaches for plumes in fractured rock conceptualized as large, diffuse, and unstructured are limited if not non-existent. Access to Contaminants Remediation at most fractured rock sites is confounded by the large ratio of contaminant in the matrix as opposed to fractures (see Chapter 3)
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From page 98... ...
Furthermore, because much of the contaminant is ultimately stored in the matrix, contact between amendments and contaminants relies on diffusion of the amendment into the matrix -- a rate-limiting step in the remediation process. FIGURE 6.3 Life stage of a DNAPL release in fractured rock.
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From page 99... ...
, four remediation approaches remain of potential interest for selected remedial goals at fractured rock sites: bioremediation, ISCO, thermal methods, and monitored natural attenuation. Biological Approaches Cost and sustainability indicators make the use of biological remediation in fractured rock attractive.
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From page 100... ...
It is reasonable, however, that biological approaches are possible and should be considered at fractured rock sites. A combination of engineered biostimulation and natural attenuation may provide effective solutions in many cases.
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From page 101... ...
The use of oxidation and reduction remediation approaches in fractured rock environments is more advanced than biological approaches, but there is still a lack of well-documented case studies, particularly for large-scale implementations. Oxidation and reduction approaches are plausible
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From page 102... ...
. Steam heating was employed at four of the six fractured rock sites, with TCH and other approaches each employed at one site.
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From page 103... ...
Low matrix permeability, high matrix porosity, and wide fracture spacing can contribute to boiling point elevation in the rock matrix. Consequently, knowledge of these properties is important for the estimation of treatment times.
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From page 104... ...
Although not documented, experience on the part of committee members indicates that pilot studies in fractured rock are often costly, difficult to design, and prone to less success than in unconsolidated porous media. Even well-designed pilot tests following significant site characterization and treatability testing (Goldstein et al., 2004; Pearson et al., 2004; Lebron et al., 2012)
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From page 105... ...
Matrix diffusion can be considered a natural attenuation process, because it attenuates the rate at which contaminants migrate in the forward direction, and it attenuates the contaminant discharge into the mobile fluid in the reverse direction. Dispersion is also a significant process occurring within fractured rock settings, particularly in crystalline rocks containing multiple hydraulically connected fracture sets resulting in the dispersion of a given contaminant through an ever increasing volume along the flow path.
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From page 106... ...
Significant benefits in terms of plume lifespan reduction are more likely through treatment of contaminant within the fractured rock matrix. Current conceptual models of contaminant distribution in fractured rock settings indicate the importance of contaminant remediation in both the matrix and fracture porosities.
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From page 107... ...
The requirement for treatment of fracture porosity along flow paths has a direct and significant correlation with complexity of remedial design, cost, and resistance from responsible parties. In the majority of cases, given the resources required for such extensive remediation and the technical difficulties of even achieving such remediation, a careful and considered assessment of the ultimate remedial goals is necessary.
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From page 108... ...
Natural attenuation is a required component of all remediation solutions in fractured rock. Because of the skewed distribution of stored contaminant toward the matrix porosity, the difficulty of treating contaminant within the matrix porosity, and the difficulties inherent in the identification and location of fluid flow within the fracture porosity, natural attenuation is likely to be
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From page 109... ...
Monitored natural attenuation may not be a suitable sole remedy in some fractured rock settings where risk to human or ecological health is severe. The occurrence of natural attenuation processes within fractured rock systems, and their demonstration at a particular site, is not necessarily sufficient for the use of monitored natural attenuation as a sole remedy (e.g., EPA, 1999a)
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From page 110... ...
could be reasonably argued to have effectively little change on contaminant concentrations and thus not be required. Such an approach is not suitable as a default position for remediation at fractured rock sites, but it may be suitable as a considered position at some sites.
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From page 111... ...
Improving practice will require aligning the goals and resources of researchers, funding agencies, regulators, site owners, and practitioners. Reduced research funding for fractured rock remediation studies leaves few options for implementing and managing a program or process to increase knowledge and improve practice.
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