Conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone

Abstract

[1998]. They designed a compartmental liquid sampler, which was inserted into a horizontal borehole, to collect infiltrating solution at multiple locations. They estimated the amount of water flowing through the fractures and imbibing into the matrix across the fracture walls and determined that under variable moisture content conditions the fracture aperture, roughness, and flow channels varied with time. They also noted that under field conditions the effective fracture aperture was more than 1 order of magnitude smaller than that expected based on laboratory conditions. Or and Ghezzehei [2000] studied water dripping into subterranean cavities in a fractured porous medium in order to improve estimates of dripping rates onto waste disposal canisters placed in caverns. These results suggest that conventional approaches and concepts, such as Darcy flow through a constant fracture aperture, may not be valid for characterizing unsaturated fractured rocks.Several laboratory-scale investigations were conducted using natural fracture cores and fracture replicas to investigate factors and processes affecting flow and transport under con- In 1996, three groups of 16 wells were drilled to install monitoring instrumentation, including vertical wells of series T (depths of 3-6.7 m), and inclined wells (270-45 ø from vertical) of series E and R (lengths of 18.3-22.9 m). In 1997, after interpretation of the results of the 1996 infiltration test, which showed a zone of preferential flow between wells R1 and R2, two additional inclined wells (R5 and R6) were drilled between existing R wells. Note that inclined boreholes were mostly drilled from the outside of the pond to reduce the disturbance to the pond surface and to intersect more vertical columnbounding fractures to better characterize the three-dimensional geometry of flow below the pond.The types of instrumentation used during the infiltration tests are summarized in Table 1. A more detailed description of the instrumentation is given by Faybishenko et al. [1998b]. All the instruments were installed in boreholes using the following method of borehole completion [Faybishenko et al., 1998d]. The instruments were attached to the outer faces of polyethylene packers mounted onto sections of 3.5-crn OD PVC manchette pipe, and the sections were glued together to form a continuous string of instruments placed at preselected depths. After the string with the probes was lowered into a borehole, the packers and the space between the packers were infilled with impermeable polyurethane resin, thus pressing the instruments against the borehole walls. This completion method ensured that no water flow occurred through the bore- small trench (15 cm high by 15 cm wide) was cut into the basalt at the location of the previous berm and a permanent concrete wall was constructed that practically eliminated water leakage beneath and through the berm. The experimental data and fitting curves are shown in Figure 6, and the fitting parameters for each test, which were determined using a lea...

Fault-matrix interactions in nonwelded tuff of the Paintbrush Group at Yucca Mountain

“…Water-release experiments into fractures in unstaturated formations have been conducted at scales extending from less than 1.0 m (e.g., Lenormand and Zarcone, 1989;Persoff and Pruess, 1995;Haldeman et al, 1991) to scales greater than 10 m (e.g., Kilbury et al, 1986;Davidson et al, 1989;Faybishenko et al, 2000). At the one-to-tenmeter scale, several in situ experiments have investigated the interplay of fracture flow and fracture matrix interactions (e.g., Wang et al, 1999;Dahan et al, 1998;Podgorney et al, 2000).…”

A deterministic methodology for prediction of fracture distribution in basaltic multiflows

“…Box Canyon was chosen for a multidisciplinary study by Lawrence Berkeley National Laboratory, INEEL, and Stanford researchers for hydrologic characterization of the fractured basalt [Faybishenko et al, 1999a[Faybishenko et al, , 1999b. The overall study integrates in situ infiltration tests for unsaturated flow, geophysical investigations, hydrological modeling, and geological characterization of the fracture system.…”

INEEL Subregional Conceptual Model Report; Volume 1 - Summary of Existing Knowledge of Natural and Anthropogenic Influences Governing Subsurface Contaminant Transport in the INEEL Subregion of the Eastern Snake River Plain

“…Because of the macro scale anisotropy, extensive lateral spreading was expected (Faybishenko et al 2000); although other researchers found vertical and horizontal hydraulic conductivity to be virtually identical for a number of core samples. Results from the infiltration test indicated that vertical permeability was significantly greater than previously assumed and that lateral spreading appeared to occur at the sedimentary interbeds and not in rubble zones between flows.…”

“…It has been 3-99 suggested that a single porosity model may not be sufficient to represent flow in fractured basalt (Faybishenko et al 2000). Other researchers have stated that "various processes are not well enough understood with respect to unsaturated-zone flow behavior to predict on a theoretical basis the effect on the spread of contamination" (USGS 1999).…”

“…Several types of preferential flow, including macropore flow, funnel flow, and fingered flow, may increase vertical and horizontal flow of water, as well as dissolved contaminants. Faybishenko et al (2000) has questioned whether a Darcian description of vadose-zone flow is adequate in a fractured media.…”