Browsing by Author "Munoz, JF"

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    A numerical model for simulation of bioremediation of hydrocarbons in aquifers
    (GROUND WATER PUBLISHING CO, 1998) Munoz, JF; Irarrazaval, MJ
    A numerical model was developed to describe the bioremediation of hydrocarbons in ground water aquifers considering aerobic degradation. The model solves the independent transport of three solutes (oxygen, hydrocarbons, and microorganisms) in ground water flow using the method of characteristics. Interactions between the three solutes, in which oxygen and hydrocarbons are consumed by microorganisms, are represented by Monod kinetics, solved using a Runge-Kutta method. Model simulations showed good correlation as compared with results of soil column experiments. The model was used to estimate the time needed to remediate the columns, which varied from one to two years.
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    Acid leaching of copper in a saturated porous material: Parameter identification and experimental validation of a two-dimensional transport model
    (ELSEVIER SCIENCE BV, 1997) Munoz, JF; Rengifo, P; Vauclin, M
    In this study, a two-dimensional mathematical solute transport model is proposed to simulate the leaching of copper ore tailings using sulfuric acid as the leaching agent, injection wells to introduce the leaching agent, and pumping wells to retrieve the pregnant copper leach solution. To calibrate the model, a tracer experiment and a leaching experiment were performed, both under conditions of a single-direction flow pattern established between two boundaries of constant height. These experiments enabled the model hydraulic, dispersion and reaction parameters to be determined. Validation of the model was performed by comparison of the numerical results given by the model with experimental results obtained from a second leaching experiment, performed under conditions of a radial flow pattern established through the use of four injection wells and one pumping well and making use of the parameters estimated previously during the calibration process, The comparison between predicted and measured leaching behavior was good (20-22% error). The study has significant implications for applications related to the use of the proposed numerical model for predicting the performance of in-situ soil washing alternatives. (C) 1997 Elsevier Science B.V.
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    Evaporation and land surface energy budget at the Salar de Atacama, Northern Chile
    (ELSEVIER SCIENCE BV, 2005) Kampf, SK; Tyler, SW; Ortiz, CA; Munoz, JF; Adkins, PL
    Playa systems are driven by evaporation processes, yet the mechanisms by which evaporation occurs through playa salt crusts are still poorly understood. In this study we examine playa evaporation as it relates to land surface energy fluxes, salt crust characteristics, groundwater and climate at the Salar de Atacama, a 3000 km(2) playa in northern Chile containing a uniquely broad range of salt crust types. Land surface energy budget measurements were taken at eight representative sites on this playa during winter (August 2001) and summer (January 2002) seasons. Measured values of net all-wave radiation were highest at vegetated and rough halite crust sites and lowest over smooth, highly reflective salt crusts. Over most of the Salar de Atacama, net radiation was dissipated by means of soil and sensible heat fluxes. Dry salt crusts tended to heat and cool very quickly, whereas soil heating and cooling occurred more gradually at wetter vegetated sites. Sensible heating was strongly linked to wind patterns, with highest sensible heat fluxes occurring on summer days with strong afternoon winds. Very little energy available at the land surface was used to evaporate water. Eddy covariance measurements could only constrain evaporation rates to within 0.1 mm d(-1), and some measured evaporation rates were less than this margin of uncertainty. Evaporation rates ranged from 0.1 to 1.1 mm d(-1) in smooth salt crusts around the margin of the salar and from 0.4 to 2.8 mm d(-1) in vegetated areas. No evaporation was detected from the rugged halite salt crust that covers the interior of the salar, though the depth to groundwater is less than 1 m in this area. These crusts therefore represent a previously unrecorded end member condition in which the salt crusts form a practically impermeable barrier to evaporation. (C) 2005 Elsevier B.V. All rights reserved.
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    Numerical modeling of saline intrusion in Salar de Atacama
    (ASCE-AMER SOC CIVIL ENGINEERS, 2003) Tejeda, I; Cienfuegos, R; Munoz, JF; Duran, M
    This paper presents the results of numerical simulations of groundwater circulation and solute transport at the Salar de Atacama through use of a numerical model to solve the two-dimensional problem of flow in an aquifer when considering the effects of variable density. The phenomena associated with solute transport are modeled by means of an advection-dispersion equation, and a linear relationship is assumed between fluid density and concentration of the dissolved solids. Simulations considered conditions of high groundwater evaporation, which depends on the depth of the phreatic surface. Results indicate that the discharge of groundwater occurs essentially in freshwater-saline water interface zones, where a number of lagunas begin. Different freshwater recharge scenarios were simulated, while it was verified that the effects of evaporation are important and minimize or buffer the variations in the phreatic surface and the discharges of groundwater that are the source of water supply for the lagunas.
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    Opus simulation of water dynamics and nitrate transport in a field plot
    (ELSEVIER SCIENCE BV, 1999) Bonilla, CA; Munoz, JF; Vauclin, M
    In this paper, Opus, an agricultural contaminant transport model, was used to simulate a year of soil water flow and nitrate transport as well as crop growth for an arable cultivated soil, near Grenoble, France. This study is explicitly related to the cultivation of irrigated maize, a major crop in the area. The results have shown that, in terms of water balance, the simulations of water flow match the general measured trends. Drainage and evapotranspiration were estimated with errors of 4 and 20%, respectively. Runoff estimation was exactly accurate. Nitrogen movement and nitrogen concentration in the root zone were simulated well, and the cumulative leach beyond the root zone was estimated with an error less than 11%. The results for crop growth were good. Some reasons for these results are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.