Grace W. Su

Experimental studies of water seepage and intermittent flow in unsaturated, rough-walled fractures

Flow visualization experiments were conducted on a transparent replica of a natural, rough-walled rock fracture from the Stripa Mine, Sweden, for inlet conditions of constant pressure and flow rate over a range of angles of inclination. The experiments demonstrated that infiltrating water proceeds through unsaturated rock fractures along nonuniform, localized preferential flow paths. Even though constant inlet conditions were maintained, pervasive unsteady or intermittent flow was also observed in these experiments, where portions of the flow channel underwent cycles of snapping and reforming. Experiments conducted on parallel plates with a sequence of apertures progressing from small to large to small reproduced intermittent flow. Measurements of the frequency of intermittent flow events and the volume of water metered between events were obtained from the fracture replica and parallel plate experiments and related to the Bond and capillary numbers to generalize the results. The frequency data from the fracture replica experiments did not follow the same trend as the data from the parallel plate experiments for similar Bond and capillary numbers, but the volume of water metered data was consistent in these experiments.

Correspondence of the Gardner and van Genuchten–Mualem relative permeability function parameters

The Gardner and van Genuchten models of relativepermeability are widely used in analytical and numerical solutions toflow problems. However, the applicab ility of the Gardner model to realproblems is usually limited, because empirical relative permeability datato calibrate the model are not routinely available. In contrast, vanGenuchten parameters can be estimated using more routinely availablematric potential and saturation data. However, the van Genuchten model isnot amenable to analytical solutions. In this paper, we introducegeneralized conversion formulae that reconcile these two models. Ingeneral, we find that the Gardner parameter alpha G is related to the vanGenuchten parameters alpha vG and n by alpha G=alpha vG ~; 1:3 n. Thisconversion rule will allow direct recasting of Gardner-based analyticalsolutions in the van Genuchten parameter space. The validity of theproposed formulae was tested by comparing the predicted relativepermeability of various porous media with measured values.

Solute transport along preferential flow paths in unsaturated fractures

Laboratory experiments were conducted to study solute transport along preferential flow paths in unsaturated, inclined fractures. Qualitative aspects of solute transport were identified in a miscible dye tracer experiment conducted in a transparent replica of a natural granite fracture. Additional experiments were conducted to measure the breakthrough curves of a conservative tracer introduced into an established preferential flow path in two different fracture replicas and a rock-replica combination. The influence of gravity was investigated by varying fracture inclination. The relationship between the travel times of the solute and the relative influence of gravity was substantially affected by two modes of intermittent flow that occurred: the snapping rivulet and the pulsating blob modes. The measured travel times of the solute were evaluated with three transfer function models: the axial dispersion, the reactors-in-series, and the lognormal models. The three models described the solute travel times nearly equally well. A mechanistic model was also formulated to describe transport when the pulsating blob mode occurred which assumed blobs of water containing solute mixed with residual pools of water along the flow path.

Preliminary studies of water seepage through rough-walled fractures

For groundwater aquifers in fractured rock, fractures play a significant role in the transport of water and contaminants through the unsaturated zone to the groundwater table. Fractures can provide preferential flow paths for infiltrating liquids that dramatically accelerate contaminant transport compared to predictions based upon spatially uniform infiltration. The actual liquid distribution during infiltration determines the contact area between the flowing water and rock, and liquid residence time, which in turn affects the potential for rock-water and rock-solute interaction, as well as mass transfer between liquid and gas phases. This report summarizes flow- visualization experiments of water percolation through transparent replicas of a natural rock fracture. We have focused on phenomenological and exploratory experiments that can lead to a conceptual model which incorporates the important physical mechanisms that control flow.

Heat as a Ground-Water Tracer at the Russian River RBF Facility, Sonoma County, California

Temperature is routinely collected as a water quality parameter, but only recently utilized as an environmental tracer of stream exchanges with ground water (Stonestrom and Constantz, 2003). In this paper, water levels and seasonal temperatures were used to estimate streambed hydraulic conductivities and water fluxes. Temperatures and water levels were analyzed from 3 observation wells near the Russian River RBF facility, north of Forestville, Sonoma County, CA. In addition, 9 shallow piezometers were installed in 3 cross-sections across the stream near a pair of collector wells at the RBF facility. Hydraulic conductivities and fluxes were estimated by matching simulated ground-water temperatures to the observed ground-water temperatures with an inverse modeling approach. Using temperature measurements in the shallow piezometers from 0.1 to 1.0 m below the channel, estimates of infiltration indicated a distinct area of streambed clogging near one of the RBF collector wells. For the deeper observation wells, temperature probes were located at depths between 3.5 m to 7.1 m below the channel. Estimated conductivities varied over an order of magnitude, with anisotropies of 5 (horizontal to vertical hydraulic conductivity) generally providing the best fit to observed temperatures.

Flow dynamics and solute transport in unsaturated rock fractures

Rock fractures play an important role in flow and contaminant transport in fractured aquifers, production of oil from petroleum reservoirs, and steam generation from geothermal reservoirs. In this dissertation, phenomenological aspects of flow in unsaturated fractures were studied in visualization experiments conducted on a transparent replica of a natural, rough-walled rock fracture for inlet conditions of constant pressure and flow rate over a range of angles of inclination. The experiments demonstrated that infiltrating liquid proceeds through unsaturated rock fractures along non-uniform, localized preferential flow paths. Even in the presence of constant boundary conditions, intermittent flow was a persistent flow feature observed, where portions of the flow channel underwent cycles of snapping and reforming. Two modes of intermittent flow were observed, the pulsating blob mode and the rivulet snapping mode. A conceptual model for the rivulet snapping mode was proposed and examined using idealized, variable-aperture fractures. The frequency of intermittent flow events was measured in several experiments and related to the capillary and Bond numbers to characterize this flow behavior.

Mobility of Tritium in Engineered and Earth Materials at the NuMIFacility, Fermilab: Progress report for work performed between June 13and September 30, 2006

This report details the work done between June 13 and September 30, 2006 by Lawrence Berkeley National Laboratory (LBNL) scientists to assist Fermi National Accelerator Laboratory (Fermilab) staff in understanding tritium transport at the Neutrino at the Main Injector (NuMI) facility. As a byproduct of beamline operation, the facility produces (among other components) tritium in engineered materials and the surrounding rock formation. Once the tritium is generated, it may be contained at the source location, migrate to other regions within the facility, or be released to the environment.

In situ freeze-capturing of fracture water using cryogenic coring

Current methods do not allow for sampling of in situ water from unsaturated fractures in low-moisture environments. A novel cryogenic coring technique based on the method developed by Simon and Cooper (1996) is used to collect in situ water in unsaturated fractures. This method uses liquid nitrogen as the drilling fluid, which can freeze the fracture water in place while coring. Laboratory experiments are conducted to demonstrate that water in an unsaturated fracture can be frozen and collected using cryogenic coring.