Investigatory Project “ Kaymito Leaves Decoction as Antiseptic Mouthwash ” Essay

Introduction1.1 riddle Statement breakings atomic number 18 prevalent in infixed and synthetic structural media, flat in the crush engineered materials. We find bankrupts in fundamental principle, in sandstone aquifers and anoint reservoirs, in clay layers and even in unconsolidated materials (Figures 1.1 to 1.4). transmutations argon to a fault common in concrete, intaked both as a structural material or as a liner for fund tanks (Figure 1.5). body liners mathematical functiond in landfills, sludge and brine judicature pits or for on a lower floorground storage tanks can recess, let go of their tranquil contents to the submersed (Figure 1.6). Even whippy materials such as asphalt demerit with sentence (Figure 1.7).The fact that cracks atomic number 18 inevitable has led to spend billions of research dollars to construct safe long-term (10,000 years or more) storage for high-level nuclear wastefulness (Savage, 1995 IAEA, 1995), both to consider which construction techniques atomic number 18 least(prenominal) likely to result in lose iture and what be the implications of a failure, in terms of release to the environment and potential contamination of ground pee descents or exposure of humans to high levels of radioactivity.Why do materials fail? In sanitary-nigh cases, the material is blemished from its genesis. In crystalline materials, it whitethorn be the cellular inclusion of one unalike atom or mite in the structure of the outgrowth crystal, or scarcely when the juncture of devil crystal planes. In depositional materials, different grain types and sizes whitethorn be laid raze, resulting in layering which hence wrenchs the initiation plane for the crevice. Most materials fail beca use of goods and services of mechanical stresses, for example the weight of the overburden, or rand so forth (Atkinson, 1989 Heard et al., 1972). Some mechanical stresses are use constantly2 until the material fails, otherwises are delivered in a abrupt event. Other causes of failure are thermal stresses, drying and out accrue cycles and chemical dissolution.After a material relegates, the deuce faces of the conk out may be subject to redundant stresses which every close or open the fracture, or may subject it to shear. Other materials may temporarily or permanently deposit in the fracture, partly or totally blocking it for subsequent unruffled less(prenominal)en. The fracture may be al around close up for millions of years, still if the material sticks exposed to the surface or near surface environment, the resulting loss of overburden or weathering may allow the fractures to open. In some cases, we are actually interested in introducing fractures in the subsurface, via hydraulic (Warpinski, 1991) or pneumatic fracturing (Schuring et al., 1995), or more mightily think ofs, to increase fluid bunk in oil reservoirs or at contaminated sites. Our particular focalize in this orbit is the role that fractures play in the movement of contaminants in the subsurface. weewee supply from fractured rudiments aquifers is common in the United States (Mutch and Scott, 1994). With increasing frequence contaminated fractured aquifers are detected (NRC, 1990). In some cases, the source of the contamination is a Non-Aqueous Phase liquefiable (NAPL) which is any in pools or as counterpoise ganglia in the fractures of the porous intercellular substance. Dissolution of the NAPL may find over several decades, resulting in a growing plume of fade away contaminants which is carryed through and through the fractured aquifer due to vivid or imposed hydraulic gradients. Fractures in aquitards may allow the seepage of contaminants, either dissolved or in their own conformation, into wet sources.Fluid ladder in the fractured porous media is of significance not only in the context of contaminant moveee, but in either case in the production of oil from reservoirs, the generation of locomote for power from geothermal reservoirs, and the prediction of structural unity or failure of large geotechnical structures, such as dams or foundations. Thus, the results of this study begin a commodious range of applications.The conceptual model of a usual contaminant spill into porous media has been put in the lead by Abriola (1989), Mercer and Cohen (1990), Kueper and McWhorter (1991) and Parker et al. (1994). In some cases, the contaminant is dissolved in weewee and thusly3 travels in a fractured aquifer or aquitard as a solute. Fractures provide a closely channel for widely distributing the contaminant throughout the aquifer and also result in contaminant transport in somewhat unpredictable instructions, depending on the fracture planes that are intersected (Hsieh et al., 1985).More typically a contaminant enters the subsurface as a liquid phase say from the gaseous or aqueous phases present (Figure 1.8). The NAPL may be leaking from a damaged or decaying storage vessel (e.g. in a gasoline displace or a refinery) or a disposition pond, or may be spilt during transport and use in a manufacturing process (e.g. during degreasing of metal parts, in the electronics industry to clean semiconductors, or in an landing field for cleaning jet engines). The NAPL travels first through the unsaturated regulate, under ternion-phase extend conditions, displacing air and water. The variations in ground substance permeability, due to the heterogeneity of the porous medium, result in additional deviations from vertical catamenia.If the NAPL encounters layers of slightly less porous materials (e.g. silt or clay lenses, or even tightly packed sand), or materials with smaller pores and thus a higher capillary entry blackjack (e.g. NAPL entering a tight, water-filled porous medium), it entrust function to flow mostly in the horizontal direction until it encounters a manner of less resistance, either more leaky or with larger pores. Microfra ctures in the ground substance are also important in allowing the NAPL to flow through these lowpermeability lenses. When the NAPL reaches the capillary fringe, both scenarios may arise. First, if the NAPL is less dense than water (LNAPL, e.g. gasoline, most hydrocarbons), then perkiness forces forget allow it to float on nip of the water table.The NAPL first moulds a small mound, which speedily string outs horizontally over the water table (Figure 1.9). When the water table rises due to recharge of the aquifer, it displaces the NAPL pool upward, but by that time the saturation of NAPL may be so low that it becomes disconnected. Disconnected NAPL will normally not flow under two-phase (water and NAPL) conditions.Connected NAPL will move up and down with the movements of the water table, cosmos smeared until becomes disconnected. If the water table goes above the disconnected NAPL, it will begin to slowly dissolve. NAPL in the unsaturated district will4 slowly modify. The rates of dissolution and volatilization are controlled by the flow of water or air, respectively (Powers et al., 1991 milling machine et al., 1990 Wilkins et al., 1995 Gierke et al, 1990). A plume of dissolved NAPL will form in the ground water, as swell as a plume of volatilized NAPL in the unsaturated zone.If the NAPL is denser than water (DNAPL, e.g. chlorinated total solvents, polychlorinated biphenyls, tars and creosotes), then once it reaches the water table it begins to form a mound and spread horizontally until either there is enough loudness to overcome the capillary entry insistence (DNAPL into a water saturated matrix) or it finds a path of less resistance into the water-saturated matrix, either a fracture or a more porous/permeable region. Once in the saturated zone, the DNAPL travels downward until either it reaches a low enough saturation to become disconnected (forming drops or ganglia) and immobile, or it finds a low-permeability layer. If the layer does not exte nd very far, the DNAPL will flow horizontally around it.In many cases, the DNAPL reaches fundamentals (Figure 1.10). The oscillate usually contains fractures into which the DNAPL flows readily, displacing water. The capillary entry pressure into most fractures is quite low, on the order of a few centimeters of DNAPL head (Kueper and McWhorter, 1991). Flow into the fractures continues until either the fracture becomes highly DNAPL saturated, or the fracture is filled or closed below, or the DNAPL spreads thin enough to become disconnected. The DNAPL may flow into horizontal fractures within the fracture internet.In terms of remediation strategies, DNAPLs in fractured bedrock are probably one of the most resolved problems ( national Research Council, 1994). They are a continuous source of dissolved contaminants for years or decades, making any pumping or active bioremediation alternative a very long term and costly proposition. Excavation down to the fractured bedrock is very exp ensive in most cases, and removal of the contaminated bedrock even more so.Potential remediation alternatives for consideration, include dewatering the contaminated zone via high-rate pumping and then applying Soil Vapor Extraction to transplant volatile DNAPLs, or applying steam to mobilize and volatilize the DNAPL towards a collection well. An additional option is to use5 surfactants, either to increase the dissolution of DNAPL or to reduce its interfacial tension and thus remobilize it (Abdul et al., 1992). An issue with remobilizing via surfactants is the potential to force the DNAPLs further down in the aquifer or bedrock, complicating the removal.If an potent remediation scheme is to be engineered, such as Soil Vapor Extraction, steam injection or surfactant-enhanced dissolution or militarization, we need to understand how DNAPLs flow through fractures. Flow may be either as a solute in the aqueous phase, as two separate phases (DNAPL-water) or as three phases (DNAPL, wate r and gas, either air or steam). other(prenominal) complication in any remediation scheme, not addressed in this study, is how to specify the fracture net wager. Which are the fractures that carry most of the flow? What is their aperture and direction? What is the slow-wittedness of fracturing in a particular medium? are the fractures connected to other fractures, probably in other planes?How does one sample enough of the subsurface to sacrifice a good idea of the complexity concern? Some techniques are beginning to emerge to determine some of the most important parameters. For example, pumping and tracer bullet tests (McKay et al., 1993 Hsieh et al., 1983) may provide enough data to determine the mean mechanical and hydraulic aperture of a fracture, as well as its main orientation. Geo somatogenetic techniques like seismic imaging, ground-penetrating radar and electrical conduction tests are macrocosm improved to assist in the determination of fracture zones (National Res earch Council, 1996).However, there is room for significant amelioration in our current ability to characterize fractures in the subsurface. Even if we come to understand how single and polyphase flow occurs in a fracture, and the interactions among the fracture and the porous matrix surrounding it, how do we get word all these phenomena in a modeling framework? Clearly, we cannot describe every fracture in a model that may consider cases of tens, hundreds or thousands of meters in one or more directions. One go up is to consider the medium as an equivalent continuum (Long, 1985), where the venial properties are somehow averaged in the macroscopic scale. probably the best solution for averaging properties is to use a stochastic description of properties such as permeability (or6 hydraulic conductivity) including the effect of fractures on overall permeability, diffusivity, sorption capacity, grain size, wettability, etc. Another approach, first developed in the crude oil in dustry, is to consider a bivalent porosity/dual permeability medium (Bai et al., 1993 Zimmerman et al., 1993 Johns and Roberts, 1991 Warren and Root, 1963), referring to the porosity and permeability of the matrix and the fracture. Diffusive or capillary forces trend the contaminants, or the oil and its components, into or out of the matrix, and most advective flow occurs in the fractures. None of these models has yet been validated through controlled experiments.1.2 Research ObjectivesThe objectives of this research are To characterize the fracture aperture distribution of several fractured porous media at high blockage To study the transport of a contaminant dissolved in water through fractured media, via experimental observation To study the physical processes involved in two- and three-phase sacks at the pore scale To go along two- and three-phase displacements in existing fractured porous media To guide the experimental observations into a modeling framework for progno stic purposes.1.3 Approach7To understand single and multiphase flow and transport processes in fractures, I first decided to characterize at a high level of contract the fracture aperture distribution of a number of fractured rock cores using CAT-scanning. With this information, I determined the geometry and permeability of the fractures, which I then use to construct a numeral flow model. I also use this information to test the validity of predictive models that are ground on the assumed statistics of the aperture distribution.For example, stochastic models (Gelhar, 1986) use the geometrical mean of the aperture distribution to predict the transmissivity of a fracture, and show that the aperture variance and correlation length can be used to predict the dispersivity of a solute through a fracture. These models have not been, to my knowledge, been tried and true experimentally prior to this study. I compare these theoretical predictions of fracture transmissivity and dispersi vity of a contaminant, with experimental results, both from the interpretation of the breakthrough snub of a non-sorbing tracer and from CAT-scans of the tracer movement through the fractured cores.To study multiphase displacements at the pore scale, we use a physical micromodel, which is a simile of a real pore space in two dimensions, etched onto a silicon substrate. The advantage of having a realistic pore space, which for the first time has the cook up pore body and pore throat dimensions in a micromodel, is that we can conform to multiphase displacements under realistic conditions in terms of the balance between capillary and viscous forces. I conduct two- and three-phase displacements to abide by the role that water and NAPL layers play in the mobilization of the various phases.The micromodels are also used to study the possible combinations of double displacements, where one phase displaces another which displaces a third phase. The pore scale observations have been captu red by Fenwick and Blunt (1996) in a threedimensional, three-phase network model which considers flow in layers and allows for double displacements. This network model then can produce three-phase proportional permeabilities as a function of phase saturation(s) and the displacement path (drainage, imbibition or a series of drainage and imbibition steps).8In addition, I use the fracture aperture information to construct capillary pressuresaturation curves for two phase (Pruess and Tsang, 1990) and three phases (Parker and Lenhard, 1987), as well as three-phase intercourse permeabilities (Parker and Lenhard, 1990). The fracture aperture distribution is also an stimulant drug to a fracture network model which I use to study two-phase displacements (drainage and imbibition) under the assumption of capillary-dominated flow.To observe two- and three-phase displacements at a larger scale, in real fractured cores, I use the CAT-scanner. I can observe the displacements at various time st eps, in permeable (e.g. sandstones) and impermeable (e.g. granites) fractured media, determining the paths that the different phases follow. These observations are then compared with the results of the network model as well as with more conventional numerical simulation.1.4 Dissertation OverviewThe work is presented in self-contained chapters. Chapter 2 deals with the high resolution measurement and subsequent statistical characterization of fracture aperture. Chapter 3 uses the fracture aperture geostatistics to predict transmissivity and diffusivity of a solute in single-phase flow through a fracture, which is then tested experimentally. We also observe the flow of a tracer inside the fracture using the CAT-scanner, and relate the observations to numerical modeling results.Chapter 4 presents the theory behind the flow characteristics at the pore scale as well as the micromodel observations of two- and three-phase flow. In Chapter 5, twophase flow in fractured and unfractured porou s media is presented, study CATscanned observations of various two-phase flow combinations (imbibition, drainage and water flooding) against numerical modeling results. Chapter 6 presents three-phase flow9 in fractures, comparing numerical results against CAT-scanner observations. Finally, Chapter 7 considers the engineering relevance of these studies.1.5 ReferencesAtkinson, B. K., 1989 Fracture Mechanics of Rock, Academic Press, New York, pp. 548 Abdul, A. S., T. L. Gibson, C. C. Ang, J. C. Smith and R. E. Sobczynski, 1992 pilot lamp test of in situ surfactant washing of polychlorinated biphenyls and oils from a contaminated site, Ground peeing, 302, 219-231Abriola, L., 1989 modelling multiphase migration of organic chemicals in groundwater systems A reappraisal and assessment, environmental Health Perspectives, 83, 117-143 Bai, M., D. Elsworth, J-C. 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Gillham, 1993 Field experiments in a fractured clay till, 1. hydraulic conductivity and fracture aperture, Water Resources Research, 294, 1149-1162 Mercer, J. W. and R. M. Cohen, 1990 A review of immiscible fluids in the subsurface properties, models, characterization and remediation, J. of contaminant Hydrology, 6, 107-163 Miller, C. T., M. M. Poirier-McNeill and A. S. Mayer, 1990 Dissolution of trapped nonaqueous phase liquids mass transfer characteristics, Water Resources Research, 2611, 2783-2796 Mutch, R. D. and J. I. Scott, 1994 Problems with the Remediation of Diffusion-Limited Fractured Rock Systems. savage Waste Site Soil Remediation possible action and Application of Innovative Technologies. New York, Marcel Dekker, Inc.National Research Council, 1994 Alternatives for ground water cleanup, National academy Press, Washington, D. 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