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Title: Advanced Vadose Zone Simulations Using TOUGH

Abstract

The vadose zone can be characterized as a complex subsurfacesystem in which intricate physical and biogeochemical processes occur inresponse to a variety of natural forcings and human activities. Thismakes it difficult to describe, understand, and predict the behavior ofthis specific subsurface system. The TOUGH nonisothermal multiphase flowsimulators are well-suited to perform advanced vadose zone studies. Theconceptual models underlying the TOUGH simulators are capable ofrepresenting features specific to the vadose zone, and of addressing avariety of coupled phenomena. Moreover, the simulators are integratedinto software tools that enable advanced data analysis, optimization, andsystem-level modeling. We discuss fundamental and computationalchallenges in simulating vadose zone processes, review recent advances inmodeling such systems, and demonstrate some capabilities of the TOUGHsuite of codes using illustrative examples.

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE
OSTI Identifier:
932699
Report Number(s):
LBNL-63367
R&D Project: GTOUGH2; BnR: YN1901000; TRN: US200813%%475
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Vadose Zone Journal; Journal Volume: 0; Journal Issue: 0; Related Information: Journal Publication Date: 2008
Country of Publication:
United States
Language:
English
Subject:
54; DATA ANALYSIS; MULTIPHASE FLOW; OPTIMIZATION; SIMULATION; SIMULATORS

Citation Formats

Finsterle, S., Doughty, C., Kowalsky, M.B., Moridis, G.J., Pan,L., Xu, T., Zhang, Y., and Pruess, K. Advanced Vadose Zone Simulations Using TOUGH. United States: N. p., 2007. Web.
Finsterle, S., Doughty, C., Kowalsky, M.B., Moridis, G.J., Pan,L., Xu, T., Zhang, Y., & Pruess, K. Advanced Vadose Zone Simulations Using TOUGH. United States.
Finsterle, S., Doughty, C., Kowalsky, M.B., Moridis, G.J., Pan,L., Xu, T., Zhang, Y., and Pruess, K. Thu . "Advanced Vadose Zone Simulations Using TOUGH". United States. doi:. https://www.osti.gov/servlets/purl/932699.
@article{osti_932699,
title = {Advanced Vadose Zone Simulations Using TOUGH},
author = {Finsterle, S. and Doughty, C. and Kowalsky, M.B. and Moridis, G.J. and Pan,L. and Xu, T. and Zhang, Y. and Pruess, K.},
abstractNote = {The vadose zone can be characterized as a complex subsurfacesystem in which intricate physical and biogeochemical processes occur inresponse to a variety of natural forcings and human activities. Thismakes it difficult to describe, understand, and predict the behavior ofthis specific subsurface system. The TOUGH nonisothermal multiphase flowsimulators are well-suited to perform advanced vadose zone studies. Theconceptual models underlying the TOUGH simulators are capable ofrepresenting features specific to the vadose zone, and of addressing avariety of coupled phenomena. Moreover, the simulators are integratedinto software tools that enable advanced data analysis, optimization, andsystem-level modeling. We discuss fundamental and computationalchallenges in simulating vadose zone processes, review recent advances inmodeling such systems, and demonstrate some capabilities of the TOUGHsuite of codes using illustrative examples.},
doi = {},
journal = {Vadose Zone Journal},
number = 0,
volume = 0,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}
  • Numerical simulators are playing an increasingly important role in advancing our fundamental understanding of hydrological systems. They are indispensable tools for managing groundwater resources, analyzing proposed and actual remediation activities at contaminated sites, optimizing recovery of oil, gas, and geothermal energy, evaluating subsurface structures and mining activities, designing monitoring systems, assessing the long-term impacts of chemical and nuclear waste disposal, and devising improved irrigation and drainage practices in agricultural areas, among many other applications. The complexity of subsurface hydrology in the vadose zone calls for sophisticated modeling codes capable of handling the strong nonlinearities involved, the interactions of coupled physical,more » chemical and biological processes, and the multiscale heterogeneities inherent in such systems. The papers in this special section of ''Vadose Zone Journal'' are illustrative of the enormous potential of such numerical simulators as applied to the vadose zone. The papers describe recent developments and applications of one particular set of codes, the TOUGH family of codes, as applied to nonisothermal flow and transport in heterogeneous porous and fractured media (http://www-esd.lbl.gov/TOUGH2). The contributions were selected from presentations given at the TOUGH Symposium 2003, which brought together developers and users of the TOUGH codes at the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, California, for three days of information exchange in May 2003 (http://www-esd.lbl.gov/TOUGHsymposium). The papers presented at the symposium covered a wide range of topics, including geothermal reservoir engineering, fracture flow and vadose zone hydrology, nuclear waste disposal, mining engineering, reactive chemical transport, environmental remediation, and gas transport. This Special Section of ''Vadose Zone Journal'' contains revised and expanded versions of selected papers from the symposium, with special attention to issues related to the vadose zone and unsaturated flow systems. The first paper, written by the original developer of TOUGH, Karsten Pruess, provides an overview of the history of the TOUGH codes, the main physical processes considered, their mathematical and numerical implementation, and case studies. That paper is followed by a review article summarizing inverse modeling applications performed by iTOUGH2. A subsequent group of papers deals with diverse unsaturated zone systems, highlighting the versatility of the code to handle a variety of processes in different geologic settings. Simulation capabilities of the TOUGH codes are increasingly used for geologic carbon sequestration studies as testified by the next group of papers. The final series of papers demonstrates the use of the TOUGH codes in support of remediation and engineering applications. These studies discuss biological and reactive chemical transport simulations, the design of clean-up operations and landfill management, and the analysis of engineered soil stabilization. As guest editors, we thank the authors for their interesting contributions, and the many reviewers for their careful and constructive review comments. Finally, on behalf of all of the authors and ourselves, we express our sincerest appreciation to Rien van Genuchten for providing the opportunity to publish these papers together in a Special Section of ''Vadose Zone Journal''.« less
  • Conceptual flow models provide a framework for predictive modeling of contaminant transport. This study tests the assumptions of steady state flow and a unit hydraulic gradient in a 177-m thick vadose zone beneath a mixed waste site, using a network of advanced tensiometers. The conceptual flow model at the waste site, located on the Idaho National Engineering Laboratory, describes moisture movement through a geologically complex site comprising basalt flows intercalated with sedimentary interbeds. The presence of sedimentary interbeds is expected to dampen and store much of the episodic recharge, resulting in near steady state conditions and unit gradient flow. Thirtymore » advanced tensiometers in 18 wells provided field water potential data at depths ranging from 6.7 to 73.5 m below land surface, beneath and adjacent to the waste site. Measured water potentials from February 2000 through August 2002 ranged from near saturation (-30°cm of water) to about –400 cm of water. Above 17 m, the observed long-term drying trends were presumed to be a response to the cumulative effect of less-than-average annual precipitation for the last three years (2000 through 2002). Below 17°m, steady state conditions were observed at over half of the monitored locations. However, long-term drying and wetting trends were also observed at 9 of the 25 monitored locations below 17 m, in contrast to the steady state flow assumptions in the conceptual model. Long-term water potential changes ranged from ~20 to 200 cm of water. It is hypothesized that these drying trends are related to areas of focused infiltration, such as drainage ditches, and are a response to decreased runoff from three years of less than average precipitation. A unit gradient was indicated, by aligning dispersed monitoring locations along a presumed vertical profile.« less
  • Soil desiccation (drying), involving water evaporation induced by dry gas injection, is a potentially robust vadose zone remediation process to limit contaminant transport through the vadose zone. A series of four intermediate-scale flow cell experiments was conducted in homogeneous and simple layered heterogeneous porous medium systems to investigate the effects of heterogeneity on desiccation of unsaturated porous media. The permeability ratios of porous medium layers ranged from about five to almost two orders of magnitude. The insulated flow cell was equipped with twenty humidity and temperature sensors and a dual-energy gamma system was used to determine water saturations at variousmore » times. The multiphase code STOMP was used to simulate the desiccation process. Results show that injected dry gas flowed predominantly in the higher permeability layer and delayed water removal from the lower permeability material. For the configurations tested, water vapor diffusion from the lower to the higher permeability zone was considerable over the duration of the experiments, resulting in much larger relative humidity values of the outgoing air than based on permeability ratios alone. Acceptable numerical matches with the experimental data were obtained when an extension of the saturation-capillary pressure relation below the residual water saturation was used. The agreements between numerical and experimental results suggest that the correct physics are implemented in the simulator and that the thermal and hydraulic properties of the porous media, flow cell wall and insulation materials were properly represented.« less
  • The information age has ushered in an awareness of and concern for global environmental problems such as climatic change, ozone depletion, deforestation, desertification, and nonpoint source (NPS) pollution. Nonpoint source pollution is the single greatest threat to surface and subsurface drinking water resources. Nonpoint source pollutants also pose a threat to sustainable agriculture, which is viewed as the most viable means of meeting the food demands of a world population that is expected to reach 9.4 billion by the middle of the next century. The ability to accurately assess present and future NPS pollution impacts on ecosystems ranging from localmore » to global scales would provide a powerful tool for environmental stewardship and guiding future human activities. Assessing NPS pollutant is a multidisciplinary problem. To address the problem, advanced information technologies and methodologies are needed that draw from all areas of science and are applied in a spatial context. It was from this setting that the 1997 Joint AGU Chapman/SSSA Outreach Conference Application of GIS, Remote Sensing, Geostatistics, and Solute Transport Modeling for Assessing Nonpoint Source Pollutants in the Vadose Zone (19--24 Oct. 1997, Riverside, CA) materialized. The objective of the conference was to examine current multidisciplinary technologies and methodologies for assessing NPS pollutants in the vadose zone, and to explore new conceptual approaches. It was the conference`s goal to provide a forum to stimulate multidisciplinary interaction to enhance the development of techniques for the real-time measurement and modeling of NPS pollution in the vadose zone and subsurface waters.« less
  • Functionally, the methods for addressing contamination must remove and/or reduce transport or toxicity of contaminants. This problem is particularly challenging in arid environments where the vadose zone can be up to hundreds of feet thick, rendering transitional excavation methods exceedingly costly and ineffective. Delivery of remedial amendments is one of the most challenging and critical aspects for all remedy-based approaches. The conventional approach for delivery is through injection of aqueous remedial solutions. However, heterogeneous vadose zone environments present hydrologic and geochemical challenges that limit the effectiveness. Because the flow of solution infiltration is dominantly controlled by gravity and suction, injectedmore » liquid preferentially percolates through highly permeable pathways, bypassing low-permeability zones which frequently contain the majority of the contamination. Moreover, the wetting front can readily mobilize and enhance contaminant transport to underlying aquifers prior to stabilization. Development of innovative, in-situ technologies may be the only way to meet remedial action objectives and long-term stewardship goals. Shear-thinning fluids (i.e., surfactants) can be used to lower the liquid surface tension and create stabile foams, which readily penetrate low permeability zones. Although surfactant foams have been utilized for subsurface mobilization efforts in the oil and gas industry, so far, the concept of using foams as a delivery mechanism for transporting reactive remedial amendments into deep vadose zone environments to stabilize metal and long-lived radionuclide contaminants has not been explored. Foam flow can be directed by pressure gradients rather than being dominated by gravity, and, foam delivery mechanisms limit the volume of water (< 20% vol.) required for remedy delivery and emplacement, thus mitigating contaminant mobilization. We will present the results of an integrated laboratory- / intermediate-scale investigation to simulate, develop, demonstrate, and monitor (using advanced geophysical techniques and natural marker monitoring) foam-based delivery of remedial amendments to stabilize metals and radionuclides in vadose zone environments.« less